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Message #12668
Re: c76ac1e6de8: MDEV-24089 support oracle syntax: rownum
Hi, Michael!
On Apr 12, Michael Widenius wrote:
> revision-id: c76ac1e6de8 (mariadb-10.5.2-551-gc76ac1e6de8)
> parent(s): a507eb17708
> author: Michael Widenius <michael.widenius@xxxxxxxxx>
> committer: Michael Widenius <michael.widenius@xxxxxxxxx>
> timestamp: 2021-03-24 19:42:24 +0200
> message:
> diff --git a/mysql-test/main/rownum.test b/mysql-test/main/rownum.test
> new file mode 100644
> index 00000000000..8d89eed2f86
> --- /dev/null
> +++ b/mysql-test/main/rownum.test
> @@ -0,0 +1,542 @@
> +--source include/have_sequence.inc
> +#
> +# Test of basic rownum() functionallity
> +# Test are done with Aria to ensure that row order is stable
what does that mean?
> +#
> +
> +CREATE OR REPLACE TABLE t1(a int, b int) engine=aria;
> +CREATE OR REPLACE TABLE t2(a int, b int) engine=aria;
> +insert into t1 values (1,10),(2,20),(3,30);
> +insert into t2 values (2,21),(3,31),(4,41);
> +
> +--echo #
> +--echo # Simple selects
> +--echo #
> +
> +select a,b,rownum() from t1;
> +select a,b,rownum() from t1 where rownum() < 2;
> +select a,b from t1 where rownum() <= 2;
> +select a,b from t1 where rownum() > 2;
> +
> +--echo #
> +--echo # Subqueries
> +--echo #
> +
> +select t1.a,rownum(),t3.a,t3.t2_rownum from t1, (select t2.a,rownum() as t2_rownum from t2 where rownum() <=2) t3;
> +select t1.a, (select t2.b from t2 where t1.a=t2.a and rownum() <= 1) 'b' from t1;
> +select t1.a, t3.a from t1, (select * from t2 where rownum() <= 2) t3;
> +select * from (select tt.*,rownum() as id from (select * from t1) tt) t3 where id>2;
> +
> +--echo #
> +--echo # Joins
> +--echo #
> +
> +select t1.a,t1.b,t2.a,t2.b,rownum() from t1,t2 where rownum() <= 4;
> +select *,rownum() from t1,t2 where t1.a=t2.a and rownum()<=2;
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()=0);
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()>1);
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()<1);
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()=1);
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()>=1);
> +
> +--echo #
> +--echo # Union
> +--echo #
> +
> +select * from t1 where rownum() <=2 union select * from t2 where rownum()<= 1;
> +
> +--echo #
> +--echo # Order by
> +--echo #
> +
> +select * from t1 where rownum() <= 2 order by a desc;
> +explain select * from t1 where rownum() <= 2 order by a desc;
> +select t1.a,t1.b,rownum() from t1 where rownum() <= 2 order by a desc;
> +explain select t1.a,t1.b,rownum() from t1 where rownum() <= 2 order by a desc;
> +select *,rownum() from t1,t2;
> +select *,rownum() from t1,t2 order by t2.a desc, t1.a desc;
> +select * from (select * from t1 order by a desc) as t where rownum() <= 2;
> +select * from t1,t2 where t1.a=t2.a and rownum()<=2 order by t1.a,t2.a;
> +
> +--echo #
> +--echo # Having
> +--echo #
> +
> +select t1.a, sum(t1.b), rownum() as 'r' from t1 group by t1.a having r <= 2;
> +--error ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE
> +select * from t1 having rownum() <= 2;
> +select t1.a, sum(t1.b), rownum() from t1 group by t1.a;
> +--error ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE
> +select t1.a, sum(t1.b), rownum() as 'r' from t1 group by t1.a having rownum() <= 2;
> +
> +--echo #
> +--echo # Sum functions
> +--echo #
> +
> +select max(rownum()),min(rownum()) from t1;
> +select sum(rownum()),avg(rownum()) from t1;
> +
> +--echo #
> +--echo # Group by
> +--echo #
> +
> +select t1.a,sum(t1.b) from t1 where rownum() < 2 group by t1.a;
> +select t1.a,sum(t2.b) from t1 JOIN t2 ON (t1.a=t2.a) where rownum() <= 2 group by t1.a;
> +select * from (select t1.a,sum(t2.b) from t1 JOIN t2 ON (t1.a=t2.a) group by t1.a) as t where rownum() <= 1;
> +select t1.a,sum(rownum()),count(*) from t1 where rownum() <= 2 group by t1.a;
> +select * from (select t1.a,sum(t1.b) from t1 group by t1.a) as t3 where rownum() < 2;
> +
> +create table t3 (a int) engine=myisam;
> +insert into t3 values (3),(5),(5),(3);
> +select a, max(rownum()) from t3 group by a;
> +drop table t3;
> +
> +CREATE TABLE t3 (
> + a int(11) DEFAULT NULL,
> + b varchar(1024) DEFAULT NULL
> +);
> +insert into t3 select mod(seq*3,20)+1, repeat(char(33+mod(seq,90)),mod(seq,10)*100) from seq_1_to_23;
> +SELECT sq.a,length(sq.f) FROM (SELECT a, GROUP_CONCAT(b,b) AS f FROM t3 GROUP BY a ORDER BY a desc) as sq WHERE ROWNUM() <= 10;
> +drop table t3;
> +
> +--echo #
> +--echo # Prepared statements
> +--echo #
> +
> +PREPARE stmt1 from "select a,b,rownum() from t1 where rownum() <= 2";
> +execute stmt1;
> +execute stmt1;
> +deallocate prepare stmt1;
> +
> +--echo #
> +--echo # Views
> +--echo #
> +
> +create view v1 as select t1.a,rownum() from t1;
> +select * from v1;
> +select t1.a,v1.* from t1,v1 where t1.a=v1.a;
> +drop view v1;
> +
> +CREATE TABLE t3 (a INT);
> +INSERT INTO t3 VALUES (1),(2),(3);
> +CREATE VIEW v1 AS SELECT a FROM t3 WHERE ROWNUM() <= 2;
> +SELECT * FROM v1;
> +drop view v1;
> +drop table t3;
> +
> +--echo #
> +--echo # Reserved words
> +--echo #
> +
> +create table t4 (a int, rownum int);
> +insert into t4 (a,rownum) values (1,2);
> +select t4.a,t4.rownum from t4;
> +drop table t4;
> +
> +--echo #
> +--echo # Test Oracle mode
> +--echo #
> +
> +set SQL_MODE=ORACLE;
> +select t1.a,rownum from t1 where rownum<=2;
> +select t1.a,rownum() from t1 where rownum()<=2;
> +--error ER_PARSE_ERROR
> +create table t4 (a int, rownum int);
> +
> +DELIMITER |;
> +DECLARE
> + CURSOR c_cursor
> + IS select a,b,rownum from t1 where rownum <= 2;
> + v_a t1.a%TYPE;
> + v_b t1.b%TYPE;
> + v_rn t1.a%TYPE;
> +BEGIN
> + OPEN c_cursor;
> + FETCH c_cursor INTO v_a, v_b, v_rn;
> + WHILE c_cursor%FOUND LOOP
> + SELECT concat(v_a,'--',v_b,'--',v_rn);
> + FETCH c_cursor INTO v_a, v_b, v_rn;
> + END LOOP;
> + CLOSE c_cursor;
> +END;|
> +DELIMITER ;|
> +
> +--error ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE
> +select a, rownum from t1 group by a, rownum having rownum < 3;
> +select a, rownum from t1 group by a, rownum having "rownum" < 3;
what's the difference between these two? Why the first is an error and the
second is not?
> +select a, rownum as r from t1 group by a, rownum having r < 3;
And the this one. Why is it not an error either?
> +
> +set SQL_MODE=DEFAULT;
> +
> +--echo # Cleanup
> +
> +drop table t1,t2;
> +
> +--echo #
> +--echo # INSERT
> +--echo #
> +
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,rownum()),(2,rownum()),(3,rownum());
> +select * from t1;
> +drop table t1;
> +
> +--echo #
> +--echo # INSERT DELAYED
> +--echo #
> +
> +create table t1 (a int not null primary key, b int);
> +insert delayed into t1 values (1,rownum()),(2,rownum()),(3,rownum());
> +select * from t1;
> +drop table t1;
> +
> +--echo #
> +--echo # INSERT ... RETURNING
> +--echo #
> +
> +create or replace table t1 (a int);
> +insert into t1 values (1),(2) returning a, rownum();
> +drop table t1;
> +
> +--echo #
> +--echo # UPDATE
> +--echo #
> +
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,2),(3,3);
> +update t1 set b=0;
> +update t1 set b=rownum()+1;
> +select * from t1;
> +
> +update t1 set b=0;
> +update t1 set b=rownum() where a < 10 and rownum() < 2;
> +select * from t1;
> +drop table t1;
> +
> +create table t1 (a int);
> +insert into t1 values (10),(20),(30);
> +update t1 set a = rownum();
> +select * from t1;
> +update t1 set a = rownum();
> +select * from t1;
> +drop table t1;
> +
> +--echo #
> +--echo # DELETE
> +--echo #
> +
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,0),(3,0);
> +delete from t1 where a < 10 and rownum() < 2;
> +select * from t1;
> +drop table t1;
> +
> +--echo #
> +--echo # MULTI-TABLE-DELETE
> +--echo #
> +
> +create table t1 (a int not null primary key);
> +insert into t1 values (1),(2),(3);
> +create table t2 (a int not null primary key);
> +insert into t2 values (1),(2),(3);
> +
> +delete t1,t2 from t1,t2 where t1.a=t2.a and rownum() <= 2;
> +select * from t1;
> +select * from t2;
> +drop table t1,t2;
> +
> +--echo #
> +--echo # MULTI-TABLE-UPDATE
> +
> +CREATE TABLE t1 (ID INT);
> +CREATE TABLE t2 (ID INT,
> + s1 TEXT, s2 TEXT, s3 VARCHAR(10), s4 TEXT, s5 VARCHAR(10));
> +
> +INSERT INTO t1 VALUES (1),(2);
> +INSERT INTO t2 VALUES (1,'test', 'test', 'test', 'test', 'test'),
> + (2,'test', 'test', 'test', 'test', 'test');
> +
> +SELECT * FROM t1 LEFT JOIN t2 USING(ID);
> +UPDATE t1 LEFT JOIN t2 USING(ID) SET s1 = 'changed';
> +select * from t2;
> +update t2 set s1="";
> +UPDATE t1 LEFT JOIN t2 USING(ID) SET s1 = 'changed' where rownum() <=1;
> +select * from t2;
> +drop table t1,t2;
> +
> +--echo #
> +--echo # LOAD DATA
> +--echo #
> +
> +create table t1 (a int, b int, c int);
> +load data infile '../../std_data/loaddata7.dat' into table t1 fields terminated by ',' lines terminated by "\r\n" (a,b) set c=rownum();
> +select * from t1;
> +drop table t1;
> +
> +--echo #
> +--echo # LIMIT OPTIMIZATION
> +--echo #
> +
> +create table t1 (a int);
> +insert into t1 select seq from seq_1_to_100;
> +
> +flush status;
> +select * from t1 where rownum() <= 3;
> +show status like "Rows_read";
> +flush status;
> +flush status;
> +select * from t1 where rownum() <= 4 and rownum() <= 3;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() < 4 and a > 10;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 3 >= rownum();
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 4 > rownum() and a > 20;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() = 1 and a > 10;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where a > 30 && 1 = rownum();
> +show status like "Rows_read";
> +flush status;
> +
> +--echo # No limit optimization
> +
> +select * from t1 where rownum() > 10;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 10 < rownum();
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() >= 10;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 10 < rownum();
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 10 <= rownum();
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where 2 = rownum();
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() = 2;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() <= 0;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() < 10 limit 4, 4;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() < 10 order by a;
> +show status like "Rows_read";
> +flush status;
> +
> +
> +--echo # rownum and limit
> +
> +select * from t1 where rownum() < 4 limit 10;
> +show status like "Rows_read";
> +flush status;
> +select * from t1 where rownum() < 10 limit 4;
> +show status like "Rows_read";
> +
> +drop table t1;
> +
> +--echo #
> +--echo # Rownum examples from Woqutech
> +--echo #
> +
> +set SQL_MODE=ORACLE;
> +create table t1 (c1 int ,c2 varchar(20)) engine=myisam;
> +insert into t1 values (1, 'aaa'),(2, 'bbb'),(3, 'ccc'),(4, 'ddd'),(5, 'eee');
> +update t1 set c2 = 'xxx' where rownum = 2;
> +select * from t1 where c2='xxx';
> +update t1 set c2 = 'xxx' where rownum < 3;
> +select * from t1 where c2='xxx';
> +delete from t1 where rownum = 2;
> +select count(*) from t1;
> +delete from t1 where rownum < 3;
> +select count(*) from t1;
> +delete from t1 where c1=rownum ;
> +select count(*) from t1;
> +delete from t1 where c1=rownum+2 ;
> +select count(*) from t1;
> +set SQL_MODE=DEFAULT;
> +drop table t1;
> +
> +--echo #
> +--echo # Rownum() used in not supported places (returns 0 or gives an error)
> +--echo #
> +
> +set @a=rownum();
> +select @a;
> +
> +--error ER_GENERATED_COLUMN_FUNCTION_IS_NOT_ALLOWED
> +create or replace table t (a int, b int as (rownum()) virtual);
> +
> +create table t1 (a int);
> +insert into t1 values (3),(1),(5),(8),(4);
> +handler t1 open;
> +--error ER_GENERATED_COLUMN_FUNCTION_IS_NOT_ALLOWED
> +handler t1 read next where rownum() < 1;
> +handler t1 close;
> +drop table t1;
> +
> +# rownum() executed in a function will be run in the function context.
> +
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,2),(3,3);
> +create function f() returns int return rownum();
> +select a, rownum(), f() from t1;
> +drop function f;
> +drop table t1;
> +
> +# rownum() executed in a trigger will be run in the function context.
> +
> +create or replace table t1 (a int, r int);
> +create trigger tr before update on t1 for each row set NEW.r = rownum();
> +insert into t1 (a) values (1),(2);
> +select * from t1;
> +update t1 set a=a+10;
> +select * from t1;
> +drop trigger tr;
> +drop table t1;
> +
> +--echo #
> +--echo # LIMIT optimisation
> +--echo #
> +
> +create table t1 (a int);
> +insert into t1 values (1),(2),(3),(4),(5);
> +
> +let $query=
> +select * from (select a from t1 where a < 1000) as tt where rownum() <= 2;
> +flush status;
> +eval $query;
> +show status like "Rows_read";
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +flush status;
> +execute stmt;
> +show status like "Rows_read";
> +flush status;
> +execute stmt;
> +show status like "Rows_read";
> +deallocate prepare stmt;
> +
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 group by a) as tt where rownum() <= 2;
> +flush status;
> +eval $query;
> +show status like "Rows_read";
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 group by a order by 1) as tt where rownum() <= 2;
> +flush status;
> +eval $query;
> +show status like "Rows_read";
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 union select 10) as tt where rownum() <= 2;
> +flush status;
> +eval $query;
> +show status like "Rows_read";
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # Other limit
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 group by a order by 1 limit 1) as tt where rownum() <= 2;
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # Other limit less
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 group by a order by 1 limit 10) as tt where rownum() <= 2;
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +let $query=
> +select * from (select a from t1 where a < 1000 union select 10 limit 1) as tt where rownum() <= 2;
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # < rownum
> +
> +let $query=
> +select * from (select a from t1 where a < 1000) as tt where rownum() < 2;
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # Simple expression
> +
> +let $query=
> +select * from (select a from t1 where a < 1000) as tt where rownum() <= 1+1;
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # Simple expression reversed
> +
> +let $query=
> +select * from (select a from t1 where a < 1000) as tt where 1+1 >= rownum();
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +--echo # expensive (no opt)
> +
> +let $query=
> +select * from (select a from t1 where a < 1000) as tt where (select max(a) from t1) >= rownum();
> +eval $query;
> +eval explain extended $query;
> +eval prepare stmt from "$query";
> +execute stmt;
> +execute stmt;
> +deallocate prepare stmt;
> +
> +drop table t1;
> diff --git a/mysql-test/main/rownum.result b/mysql-test/main/rownum.result
> new file mode 100644
> index 00000000000..e7ea92e5dde
> --- /dev/null
> +++ b/mysql-test/main/rownum.result
> @@ -0,0 +1,925 @@
> +CREATE OR REPLACE TABLE t1(a int, b int) engine=aria;
> +CREATE OR REPLACE TABLE t2(a int, b int) engine=aria;
> +insert into t1 values (1,10),(2,20),(3,30);
> +insert into t2 values (2,21),(3,31),(4,41);
> +#
> +# Simple selects
> +#
> +select a,b,rownum() from t1;
> +a b rownum()
> +1 10 1
> +2 20 2
> +3 30 3
> +select a,b,rownum() from t1 where rownum() < 2;
> +a b rownum()
> +1 10 1
> +select a,b from t1 where rownum() <= 2;
> +a b
> +1 10
> +2 20
> +select a,b from t1 where rownum() > 2;
> +a b
> +#
> +# Subqueries
> +#
> +select t1.a,rownum(),t3.a,t3.t2_rownum from t1, (select t2.a,rownum() as t2_rownum from t2 where rownum() <=2) t3;
> +a rownum() a t2_rownum
> +1 1 2 1
> +1 2 3 2
> +2 3 2 1
> +2 4 3 2
> +3 5 2 1
> +3 6 3 2
> +select t1.a, (select t2.b from t2 where t1.a=t2.a and rownum() <= 1) 'b' from t1;
> +a b
> +1 NULL
> +2 21
> +3 31
> +select t1.a, t3.a from t1, (select * from t2 where rownum() <= 2) t3;
> +a a
> +1 2
> +1 3
> +2 2
> +2 3
> +3 2
> +3 3
> +select * from (select tt.*,rownum() as id from (select * from t1) tt) t3 where id>2;
> +a b id
> +3 30 3
> +#
> +# Joins
> +#
> +select t1.a,t1.b,t2.a,t2.b,rownum() from t1,t2 where rownum() <= 4;
> +a b a b rownum()
> +1 10 2 21 1
> +2 20 2 21 2
> +3 30 2 21 3
> +1 10 3 31 4
> +select *,rownum() from t1,t2 where t1.a=t2.a and rownum()<=2;
> +a b a b rownum()
> +2 20 2 21 1
> +3 30 3 31 2
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()=0);
> +a b a b
> +1 10 NULL NULL
> +2 20 NULL NULL
> +3 30 NULL NULL
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()>1);
> +a b a b
> +1 10 NULL NULL
> +2 20 NULL NULL
> +3 30 NULL NULL
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()<1);
> +a b a b
> +1 10 NULL NULL
> +2 20 NULL NULL
> +3 30 NULL NULL
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()=1);
> +a b a b
> +2 20 2 21
> +1 10 NULL NULL
> +3 30 NULL NULL
> +select * from t1 left join t2 on (t2.a=t1.a and rownum()>=1);
> +a b a b
> +2 20 2 21
> +3 30 3 31
> +1 10 NULL NULL
> +#
> +# Union
> +#
> +select * from t1 where rownum() <=2 union select * from t2 where rownum()<= 1;
> +a b
> +1 10
> +2 20
> +2 21
> +#
> +# Order by
> +#
> +select * from t1 where rownum() <= 2 order by a desc;
> +a b
> +2 20
> +1 10
> +explain select * from t1 where rownum() <= 2 order by a desc;
> +id select_type table type possible_keys key key_len ref rows Extra
> +1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using where; Using filesort
> +select t1.a,t1.b,rownum() from t1 where rownum() <= 2 order by a desc;
> +a b rownum()
> +2 20 2
> +1 10 1
> +explain select t1.a,t1.b,rownum() from t1 where rownum() <= 2 order by a desc;
> +id select_type table type possible_keys key key_len ref rows Extra
> +1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using where; Using temporary; Using filesort
> +select *,rownum() from t1,t2;
> +a b a b rownum()
> +1 10 2 21 1
> +2 20 2 21 2
> +3 30 2 21 3
> +1 10 3 31 4
> +2 20 3 31 5
> +3 30 3 31 6
> +1 10 4 41 7
> +2 20 4 41 8
> +3 30 4 41 9
> +select *,rownum() from t1,t2 order by t2.a desc, t1.a desc;
> +a b a b rownum()
> +3 30 4 41 9
> +2 20 4 41 8
> +1 10 4 41 7
> +3 30 3 31 6
> +2 20 3 31 5
> +1 10 3 31 4
> +3 30 2 21 3
> +2 20 2 21 2
> +1 10 2 21 1
> +select * from (select * from t1 order by a desc) as t where rownum() <= 2;
> +a b
> +3 30
> +2 20
> +select * from t1,t2 where t1.a=t2.a and rownum()<=2 order by t1.a,t2.a;
> +a b a b
> +2 20 2 21
> +3 30 3 31
> +#
> +# Having
> +#
> +select t1.a, sum(t1.b), rownum() as 'r' from t1 group by t1.a having r <= 2;
> +a sum(t1.b) r
> +1 10 1
> +2 20 2
> +select * from t1 having rownum() <= 2;
> +ERROR HY000: Function 'rownum()' cannot be used in the HAVING clause
> +select t1.a, sum(t1.b), rownum() from t1 group by t1.a;
> +a sum(t1.b) rownum()
> +1 10 1
> +2 20 2
> +3 30 3
> +select t1.a, sum(t1.b), rownum() as 'r' from t1 group by t1.a having rownum() <= 2;
> +ERROR HY000: Function 'rownum()' cannot be used in the HAVING clause
> +#
> +# Sum functions
> +#
> +select max(rownum()),min(rownum()) from t1;
> +max(rownum()) min(rownum())
> +3 1
> +select sum(rownum()),avg(rownum()) from t1;
> +sum(rownum()) avg(rownum())
> +6 2.0000
> +#
> +# Group by
> +#
> +select t1.a,sum(t1.b) from t1 where rownum() < 2 group by t1.a;
> +a sum(t1.b)
> +1 10
> +select t1.a,sum(t2.b) from t1 JOIN t2 ON (t1.a=t2.a) where rownum() <= 2 group by t1.a;
> +a sum(t2.b)
> +2 21
> +3 31
> +select * from (select t1.a,sum(t2.b) from t1 JOIN t2 ON (t1.a=t2.a) group by t1.a) as t where rownum() <= 1;
> +a sum(t2.b)
> +2 21
> +select t1.a,sum(rownum()),count(*) from t1 where rownum() <= 2 group by t1.a;
> +a sum(rownum()) count(*)
> +1 1 1
> +2 2 1
> +select * from (select t1.a,sum(t1.b) from t1 group by t1.a) as t3 where rownum() < 2;
> +a sum(t1.b)
> +1 10
> +create table t3 (a int) engine=myisam;
> +insert into t3 values (3),(5),(5),(3);
> +select a, max(rownum()) from t3 group by a;
> +a max(rownum())
> +3 4
> +5 3
> +drop table t3;
> +CREATE TABLE t3 (
> +a int(11) DEFAULT NULL,
> +b varchar(1024) DEFAULT NULL
> +);
> +insert into t3 select mod(seq*3,20)+1, repeat(char(33+mod(seq,90)),mod(seq,10)*100) from seq_1_to_23;
> +SELECT sq.a,length(sq.f) FROM (SELECT a, GROUP_CONCAT(b,b) AS f FROM t3 GROUP BY a ORDER BY a desc) as sq WHERE ROWNUM() <= 10;
> +a length(sq.f)
> +20 600
> +19 1200
> +18 1800
> +17 400
> +16 1000
> +15 1600
> +14 200
> +13 800
> +12 1400
> +11 0
> +drop table t3;
> +#
> +# Prepared statements
> +#
> +PREPARE stmt1 from "select a,b,rownum() from t1 where rownum() <= 2";
> +execute stmt1;
> +a b rownum()
> +1 10 1
> +2 20 2
> +execute stmt1;
> +a b rownum()
> +1 10 1
> +2 20 2
> +deallocate prepare stmt1;
> +#
> +# Views
> +#
> +create view v1 as select t1.a,rownum() from t1;
> +select * from v1;
> +a rownum()
> +1 1
> +2 2
> +3 3
> +select t1.a,v1.* from t1,v1 where t1.a=v1.a;
> +a a rownum()
> +1 1 1
> +2 2 2
> +3 3 3
> +drop view v1;
> +CREATE TABLE t3 (a INT);
> +INSERT INTO t3 VALUES (1),(2),(3);
> +CREATE VIEW v1 AS SELECT a FROM t3 WHERE ROWNUM() <= 2;
> +SELECT * FROM v1;
> +a
> +1
> +2
> +drop view v1;
> +drop table t3;
> +#
> +# Reserved words
> +#
> +create table t4 (a int, rownum int);
> +insert into t4 (a,rownum) values (1,2);
> +select t4.a,t4.rownum from t4;
> +a rownum
> +1 2
> +drop table t4;
> +#
> +# Test Oracle mode
> +#
> +set SQL_MODE=ORACLE;
> +select t1.a,rownum from t1 where rownum<=2;
> +a rownum
> +1 1
> +2 2
> +select t1.a,rownum() from t1 where rownum()<=2;
> +a rownum()
> +1 1
> +2 2
> +create table t4 (a int, rownum int);
> +ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'rownum int)' at line 1
> +DECLARE
> +CURSOR c_cursor
> +IS select a,b,rownum from t1 where rownum <= 2;
> +v_a t1.a%TYPE;
> +v_b t1.b%TYPE;
> +v_rn t1.a%TYPE;
> +BEGIN
> +OPEN c_cursor;
> +FETCH c_cursor INTO v_a, v_b, v_rn;
> +WHILE c_cursor%FOUND LOOP
> +SELECT concat(v_a,'--',v_b,'--',v_rn);
> +FETCH c_cursor INTO v_a, v_b, v_rn;
> +END LOOP;
> +CLOSE c_cursor;
> +END;|
> +concat(v_a,'--',v_b,'--',v_rn)
> +1--10--1
> +concat(v_a,'--',v_b,'--',v_rn)
> +2--20--2
> +select a, rownum from t1 group by a, rownum having rownum < 3;
> +ERROR HY000: Function 'rownum()' cannot be used in the HAVING clause
> +select a, rownum as r from t1 group by a, rownum having r < 3;
> +a r
> +1 1
> +2 2
> +select a, rownum from t1 group by a, rownum having "rownum" < 3;
> +a rownum
> +1 1
> +2 2
> +set SQL_MODE=DEFAULT;
> +# Cleanup
> +drop table t1,t2;
> +#
> +# INSERT
> +#
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,rownum()),(2,rownum()),(3,rownum());
> +select * from t1;
> +a b
> +1 1
> +2 2
> +3 3
> +drop table t1;
> +#
> +# INSERT DELAYED
> +#
> +create table t1 (a int not null primary key, b int);
> +insert delayed into t1 values (1,rownum()),(2,rownum()),(3,rownum());
> +select * from t1;
> +a b
> +1 1
> +2 2
> +3 3
> +drop table t1;
> +#
> +# INSERT ... RETURNING
> +#
> +create or replace table t1 (a int);
> +insert into t1 values (1),(2) returning a, rownum();
> +a rownum()
> +1 1
> +2 2
> +drop table t1;
> +#
> +# UPDATE
> +#
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,2),(3,3);
> +update t1 set b=0;
> +update t1 set b=rownum()+1;
> +select * from t1;
> +a b
> +1 2
> +2 3
> +3 4
> +update t1 set b=0;
> +update t1 set b=rownum() where a < 10 and rownum() < 2;
> +select * from t1;
> +a b
> +1 1
> +2 0
> +3 0
> +drop table t1;
> +create table t1 (a int);
> +insert into t1 values (10),(20),(30);
> +update t1 set a = rownum();
> +select * from t1;
> +a
> +1
> +2
> +3
> +update t1 set a = rownum();
> +select * from t1;
> +a
> +1
> +2
> +3
> +drop table t1;
> +#
> +# DELETE
> +#
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,0),(3,0);
> +delete from t1 where a < 10 and rownum() < 2;
> +select * from t1;
> +a b
> +2 0
> +3 0
> +drop table t1;
> +#
> +# MULTI-TABLE-DELETE
> +#
> +create table t1 (a int not null primary key);
> +insert into t1 values (1),(2),(3);
> +create table t2 (a int not null primary key);
> +insert into t2 values (1),(2),(3);
> +delete t1,t2 from t1,t2 where t1.a=t2.a and rownum() <= 2;
> +select * from t1;
> +a
> +3
> +select * from t2;
> +a
> +3
> +drop table t1,t2;
> +#
> +# MULTI-TABLE-UPDATE
> +CREATE TABLE t1 (ID INT);
> +CREATE TABLE t2 (ID INT,
> +s1 TEXT, s2 TEXT, s3 VARCHAR(10), s4 TEXT, s5 VARCHAR(10));
> +INSERT INTO t1 VALUES (1),(2);
> +INSERT INTO t2 VALUES (1,'test', 'test', 'test', 'test', 'test'),
> +(2,'test', 'test', 'test', 'test', 'test');
> +SELECT * FROM t1 LEFT JOIN t2 USING(ID);
> +ID s1 s2 s3 s4 s5
> +1 test test test test test
> +2 test test test test test
> +UPDATE t1 LEFT JOIN t2 USING(ID) SET s1 = 'changed';
> +select * from t2;
> +ID s1 s2 s3 s4 s5
> +1 changed test test test test
> +2 changed test test test test
> +update t2 set s1="";
> +UPDATE t1 LEFT JOIN t2 USING(ID) SET s1 = 'changed' where rownum() <=1;
> +select * from t2;
> +ID s1 s2 s3 s4 s5
> +1 changed test test test test
> +2 test test test test
> +drop table t1,t2;
> +#
> +# LOAD DATA
> +#
> +create table t1 (a int, b int, c int);
> +load data infile '../../std_data/loaddata7.dat' into table t1 fields terminated by ',' lines terminated by "\r\n" (a,b) set c=rownum();
> +select * from t1;
> +a b c
> +2 2 1
> +3 3 2
> +4 4 3
> +5 5 4
> +6 6 5
> +drop table t1;
> +#
> +# LIMIT OPTIMIZATION
> +#
> +create table t1 (a int);
> +insert into t1 select seq from seq_1_to_100;
> +flush status;
> +select * from t1 where rownum() <= 3;
> +a
> +1
> +2
> +3
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 3
> +flush status;
> +flush status;
why twice?
> +select * from t1 where rownum() <= 4 and rownum() <= 3;
> +a
> +1
> +2
> +3
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 3
> +flush status;
> +select * from t1 where rownum() < 4 and a > 10;
> +a
> +11
> +12
> +13
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 13
> +flush status;
> +select * from t1 where 3 >= rownum();
> +a
> +1
> +2
> +3
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 3
> +flush status;
> +select * from t1 where 4 > rownum() and a > 20;
> +a
> +21
> +22
> +23
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 23
> +flush status;
> +select * from t1 where rownum() = 1 and a > 10;
> +a
> +11
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 11
> +flush status;
> +select * from t1 where a > 30 && 1 = rownum();
> +a
> +31
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 31
> +flush status;
> +# No limit optimization
> +select * from t1 where rownum() > 10;
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
You could've optimized it to `limit 0`
but I guess it's not a particularly common use case
> +flush status;
> +select * from t1 where 10 < rownum();
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where rownum() >= 10;
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where 10 < rownum();
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where 10 <= rownum();
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where 2 = rownum();
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where rownum() = 2;
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where rownum() <= 0;
> +a
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +select * from t1 where rownum() < 10 limit 4, 4;
can you add a test for `select a, rownum() from t1 limit 4, 4` please ?
> +a
> +5
> +6
> +7
> +8
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 8
> +flush status;
> +select * from t1 where rownum() < 10 order by a;
> +a
> +1
> +2
> +3
> +4
> +5
> +6
> +7
> +8
> +9
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 100
> +flush status;
> +# rownum and limit
> +select * from t1 where rownum() < 4 limit 10;
> +a
> +1
> +2
> +3
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 3
> +flush status;
> +select * from t1 where rownum() < 10 limit 4;
> +a
> +1
> +2
> +3
> +4
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 4
> +drop table t1;
> +#
> +# Rownum examples from Woqutech
> +#
> +set SQL_MODE=ORACLE;
> +create table t1 (c1 int ,c2 varchar(20)) engine=myisam;
> +insert into t1 values (1, 'aaa'),(2, 'bbb'),(3, 'ccc'),(4, 'ddd'),(5, 'eee');
> +update t1 set c2 = 'xxx' where rownum = 2;
> +select * from t1 where c2='xxx';
> +c1 c2
> +update t1 set c2 = 'xxx' where rownum < 3;
> +select * from t1 where c2='xxx';
> +c1 c2
> +1 xxx
> +2 xxx
> +delete from t1 where rownum = 2;
> +select count(*) from t1;
> +count(*)
> +5
> +delete from t1 where rownum < 3;
> +select count(*) from t1;
> +count(*)
> +3
> +delete from t1 where c1=rownum ;
> +select count(*) from t1;
> +count(*)
> +3
> +delete from t1 where c1=rownum+2 ;
> +select count(*) from t1;
> +count(*)
> +0
> +set SQL_MODE=DEFAULT;
> +drop table t1;
> +#
> +# Rownum() used in not supported places (returns 0 or gives an error)
> +#
> +set @a=rownum();
> +select @a;
> +@a
> +0
> +create or replace table t (a int, b int as (rownum()) virtual);
> +ERROR HY000: Function or expression 'rownum()' cannot be used in the GENERATED ALWAYS AS clause of `b`
> +create table t1 (a int);
> +insert into t1 values (3),(1),(5),(8),(4);
> +handler t1 open;
> +handler t1 read next where rownum() < 1;
> +ERROR HY000: Function or expression 'rownum()' cannot be used in the WHERE clause of `HANDLER`
why is that? `handler t1 read next limit 2` works just fine.
> +handler t1 close;
> +drop table t1;
> +create table t1 (a int not null primary key, b int);
> +insert into t1 values (1,1),(2,2),(3,3);
> +create function f() returns int return rownum();
> +select a, rownum(), f() from t1;
> +a rownum() f()
> +1 1 0
> +2 2 0
> +3 3 0
> +drop function f;
> +drop table t1;
> +create or replace table t1 (a int, r int);
> +create trigger tr before update on t1 for each row set NEW.r = rownum();
> +insert into t1 (a) values (1),(2);
> +select * from t1;
> +a r
> +1 NULL
> +2 NULL
> +update t1 set a=a+10;
> +select * from t1;
> +a r
> +11 0
> +12 0
> +drop trigger tr;
> +drop table t1;
> +#
> +# LIMIT optimisation
> +#
> +create table t1 (a int);
> +insert into t1 values (1),(2),(3),(4),(5);
> +flush status;
> +select * from (select a from t1 where a < 1000) as tt where rownum() <= 2;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 2
> +explain extended select * from (select a from t1 where a < 1000) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 limit 2) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000) as tt where rownum() <= 2";
> +flush status;
> +execute stmt;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 2
> +flush status;
> +execute stmt;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 2
> +deallocate prepare stmt;
> +flush status;
> +select * from (select a from t1 where a < 1000 group by a) as tt where rownum() <= 2;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 5
> +explain extended select * from (select a from t1 where a < 1000 group by a) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where; Using temporary; Using filesort
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 group by `test`.`t1`.`a` limit 2) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 group by a) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +flush status;
> +select * from (select a from t1 where a < 1000 group by a order by 1) as tt where rownum() <= 2;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 5
> +explain extended select * from (select a from t1 where a < 1000 group by a order by 1) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where; Using temporary; Using filesort
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 group by `test`.`t1`.`a` order by 1 limit 2) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 group by a order by 1) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +flush status;
> +select * from (select a from t1 where a < 1000 union select 10) as tt where rownum() <= 2;
> +a
> +1
> +2
> +show status like "Rows_read";
> +Variable_name Value
> +Rows_read 5
> +explain extended select * from (select a from t1 where a < 1000 union select 10) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +3 UNION NULL NULL NULL NULL NULL NULL NULL NULL No tables used
> +NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL NULL
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 union /* select#3 */ select 10 AS `10` limit 2) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 union select 10) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +# Other limit
> +select * from (select a from t1 where a < 1000 group by a order by 1 limit 1) as tt where rownum() <= 2;
> +a
> +1
> +explain extended select * from (select a from t1 where a < 1000 group by a order by 1 limit 1) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where; Using temporary; Using filesort
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 group by `test`.`t1`.`a` order by 1 limit 1) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 group by a order by 1 limit 1) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +execute stmt;
> +a
> +1
> +deallocate prepare stmt;
> +# Other limit less
> +select * from (select a from t1 where a < 1000 group by a order by 1 limit 10) as tt where rownum() <= 2;
> +a
> +1
> +2
> +explain extended select * from (select a from t1 where a < 1000 group by a order by 1 limit 10) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where; Using temporary; Using filesort
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 group by `test`.`t1`.`a` order by 1 limit 2) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 group by a order by 1 limit 10) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +select * from (select a from t1 where a < 1000 union select 10 limit 1) as tt where rownum() <= 2;
> +a
> +1
> +explain extended select * from (select a from t1 where a < 1000 union select 10 limit 1) as tt where rownum() <= 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 5 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +3 UNION NULL NULL NULL NULL NULL NULL NULL NULL No tables used
> +NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL NULL
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 union /* select#3 */ select 10 AS `10` limit 1) `tt` where rownum() <= 2
> +prepare stmt from "select * from (select a from t1 where a < 1000 union select 10 limit 1) as tt where rownum() <= 2";
> +execute stmt;
> +a
> +1
> +execute stmt;
> +a
> +1
> +deallocate prepare stmt;
> +# < rownum
> +select * from (select a from t1 where a < 1000) as tt where rownum() < 2;
> +a
> +1
> +explain extended select * from (select a from t1 where a < 1000) as tt where rownum() < 2;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 limit 1) `tt` where rownum() < 2
> +prepare stmt from "select * from (select a from t1 where a < 1000) as tt where rownum() < 2";
> +execute stmt;
> +a
> +1
> +execute stmt;
> +a
> +1
> +deallocate prepare stmt;
> +# Simple expression
> +select * from (select a from t1 where a < 1000) as tt where rownum() <= 1+1;
> +a
> +1
> +2
> +explain extended select * from (select a from t1 where a < 1000) as tt where rownum() <= 1+1;
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 limit 2) `tt` where rownum() <= <cache>(1 + 1)
> +prepare stmt from "select * from (select a from t1 where a < 1000) as tt where rownum() <= 1+1";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +# Simple expression reversed
> +select * from (select a from t1 where a < 1000) as tt where 1+1 >= rownum();
> +a
> +1
> +2
> +explain extended select * from (select a from t1 where a < 1000) as tt where 1+1 >= rownum();
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000 limit 2) `tt` where <cache>(1 + 1) >= rownum()
> +prepare stmt from "select * from (select a from t1 where a < 1000) as tt where 1+1 >= rownum()";
> +execute stmt;
> +a
> +1
> +2
> +execute stmt;
> +a
> +1
> +2
> +deallocate prepare stmt;
> +# expensive (no opt)
> +select * from (select a from t1 where a < 1000) as tt where (select max(a) from t1) >= rownum();
> +a
> +1
> +2
> +3
> +4
> +5
> +explain extended select * from (select a from t1 where a < 1000) as tt where (select max(a) from t1) >= rownum();
> +id select_type table type possible_keys key key_len ref rows filtered Extra
> +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 5 100.00 Using where
> +3 SUBQUERY t1 ALL NULL NULL NULL NULL 5 100.00
> +2 DERIVED t1 ALL NULL NULL NULL NULL 5 100.00 Using where
> +Warnings:
> +Note 1003 /* select#1 */ select `tt`.`a` AS `a` from (/* select#2 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` < 1000) `tt` where (/* select#3 */ select max(`test`.`t1`.`a`) from `test`.`t1`) >= rownum()
> +prepare stmt from "select * from (select a from t1 where a < 1000) as tt where (select max(a) from t1) >= rownum()";
> +execute stmt;
> +a
> +1
> +2
> +3
> +4
> +5
> +execute stmt;
> +a
> +1
> +2
> +3
> +4
> +5
> +deallocate prepare stmt;
> +drop table t1;
> diff --git a/sql/filesort.h b/sql/filesort.h
> index 29ae5e20cc6..806a4a8b027 100644
> --- a/sql/filesort.h
> +++ b/sql/filesort.h
> @@ -44,24 +44,21 @@ class Filesort: public Sql_alloc
> /** Number of records to return */
> ha_rows limit;
> /** ORDER BY list with some precalculated info for filesort */
> + ha_rows *accepted_rows; /* For ROWNUM */
> SORT_FIELD *sortorder;
first, I suspect that you want to put your accepted_rows declaration
before the comment that applies to sortorder.
second, could you do a bit more than just "For ROWNUM"?
why do you need something "for ROWNUM" inside Filesort?
> /** select to use for getting records */
> SQL_SELECT *select;
> +
> /** TRUE <=> free select on destruction */
> bool own_select;
> - /** true means we are using Priority Queue for order by with limit. */
> + /** TRUE means we are using Priority Queue for order by with limit. */
> bool using_pq;
> -
> /*
> TRUE means sort operation must produce table rowids.
> FALSE means that it halso has an option of producing {sort_key,
> addon_fields} pairs.
> */
> bool sort_positions;
> -
> - Filesort_tracker *tracker;
> - Sort_keys *sort_keys;
> -
> /*
> TRUE means all the fields of table of whose bitmap read_set is set
> need to be read while reading records in the sort buffer.
> diff --git a/sql/item_func.h b/sql/item_func.h
> index 53c236bbce7..c237fcd9ecc 100644
> --- a/sql/item_func.h
> +++ b/sql/item_func.h
> @@ -2125,6 +2125,63 @@ class Item_func_rand :public Item_real_func
> };
>
>
> +class Item_func_rownum :public Item_longlong_func
> +{
> + /*
> + This points to a variable that contains the number of rows
> + accpted so far in the result set
> + */
> + ha_rows *accepted_rows;
> + SELECT_LEX *select;
> +public:
> + Item_func_rownum(THD *thd);
> + longlong val_int() override;
> + LEX_CSTRING func_name_cstring() const override
> + {
> + static LEX_CSTRING name= {STRING_WITH_LEN("rownum") };
> + return name;
> + }
> + enum Functype functype() const override { return ROWNUM_FUNC; }
> + void update_used_tables() override {}
> + bool const_item() const override { return 0; }
> + void fix_after_optimize(THD *thd) override;
> + bool fix_fields(THD* thd, Item **ref) override;
> + bool fix_length_and_dec() override
> + {
> + unsigned_flag= 1;
> + used_tables_cache= RAND_TABLE_BIT;
> + const_item_cache=0;
> + set_maybe_null();
how can rownum be NULL?
> + return FALSE;
> + }
> + void cleanup() override
> + {
> + Item_longlong_func::cleanup();
> + /* Ensure we don't point to freed memory */
> + accepted_rows= 0;
> + }
> + bool check_vcol_func_processor(void *arg) override
> + {
> + return mark_unsupported_function(func_name(), "()", arg,
> + VCOL_IMPOSSIBLE);
> + }
> + bool check_handler_func_processor(void *arg) override
> + {
> + return mark_unsupported_function(func_name(), "()", arg,
> + VCOL_IMPOSSIBLE);
first, as I wrote above, I think that there's no logical reason why rownum should
not with with handler.
but even if it doesn't, it's much better to check for SQLCOM_HA_READ
from Item_func_rownum::fix_fields instead of traversing the whole
item tree for every single HANDLER READ command looking for Item_func_rownum
that nobody (literally, not a single user out of all our millions) will use there.
> + }
> + Item *get_copy(THD *thd) override
> + {
> + return this;
It looks wrong. We don't have any other Item that returns `this` here.
I think rownum cannot be pushed down because of RAND_TABLE_BIT,
So better return NULL here, meaning "cannot be pushed down".
Instead of `this` meaning "if you push it down, it'll surreptitiously
start corrupting the memory"
> + }
> + /* This function is used in insert, update and delete */
> + void store_pointer_to_row_counter(ha_rows *row_counter)
So this isn't a virtual method, and to use it you downcast after checking
type() == FUNC_ITEM and functype() == ROWNUM_FUNC. To avoid adding a new
virtual method thus blowing up the vtable, I presume.
And fix_after_optimize() is virtual. To avoid error-prone downcasting, would
be my guess.
Can you explain when you use what approach, please?
> + {
> + accepted_rows= row_counter;
> + }
> +};
> +
> +
> class Item_func_sign :public Item_long_func
> {
> bool check_arguments() const override
> diff --git a/sql/item_func.cc b/sql/item_func.cc
> index 25714dda03c..1165b87356a 100644
> --- a/sql/item_func.cc
> +++ b/sql/item_func.cc
> @@ -7206,3 +7206,72 @@ void Item_func_setval::print(String *str, enum_query_type query_type)
> str->append_ulonglong(round);
> str->append(')');
> }
> +
> +
> +/*
> + Return how many row combinations has accepted so far + 1
> +
> + The + 1 is to ensure that 'WHERE ROWNUM <=1' returns one row
this is a very weird explanation, it sounds as if it's
a heuristical a hack for ROWNUM <=1 to work
Why not to write "+1 takes into account the currently computed row"
> +*/
> +
> +longlong Item_func_rownum::val_int()
> +{
> + if (!accepted_rows)
> + {
> + /*
> + Rownum is not properly set up. Probably used in wrong context when
> + it should not be used. In this case returning 0 is probably the best
> + solution.
> + */
DBUG_ASSERT(0); here?
> + return 0;
> + }
> + return (longlong) *accepted_rows+1;
> +}
> +
> +
> +Item_func_rownum::Item_func_rownum(THD *thd):
> + Item_longlong_func(thd),accepted_rows(0)
> +{
> + /*
> + Remember the select context.
> + Add the function to the list fix_after_optimize in the select context
> + so that we can easily initializef all rownum functions with the pointers
> + to the row counters.
> + */
> + select= thd->lex->current_select;
> + select->fix_after_optimize.push_back(this, thd->mem_root);
> +
> + /*
> + Mark that query is using rownum() and ensure that this select is
> + not merged with other selects
> + */
> + select->with_rownum= 1;
> + thd->lex->with_rownum= 1;
> + thd->lex->uncacheable(UNCACHEABLE_RAND);
Why? ROWNUM doesn't make a query uncacheable, it's perfectly
deterministic and repeatable.
> +
> + /* If this command changes data, mark it as unsafe for statement logging */
> + if (sql_command_flags[thd->lex->sql_command] &
> + (CF_UPDATES_DATA | CF_DELETES_DATA))
> + thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
Why? It's the same as LIMIT. unsafe without ORDER BY and perfectly safe with.
> +}
> +
> +
> +bool Item_func_rownum::fix_fields(THD* thd, Item **ref)
> +{
> + if (select->having_fix_field)
> + {
> + my_error(ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE, MYF(0),
> + "rownum()", "HAVING");
> + return 1;
> + }
> + return Item_longlong_func::fix_fields(thd, ref);
> +}
> +
> +/*
> + Store a reference to the variable that contains number of accepted rows
> +*/
> +
> +void Item_func_rownum::fix_after_optimize(THD *thd)
> +{
> + accepted_rows= &select->join->accepted_rows;
why do you need both that and fix_rownum_pointers()?
I'd think that the latter alone would be sufficient
> +}
> diff --git a/sql/share/errmsg-utf8.txt b/sql/share/errmsg-utf8.txt
> index badaaa17716..aecb00563f7 100644
> --- a/sql/share/errmsg-utf8.txt
> +++ b/sql/share/errmsg-utf8.txt
> @@ -7973,3 +7973,5 @@ ER_DATA_WAS_COMMITED_UNDER_ROLLBACK
> eng "Engine %s does not support rollback. Changes were committed during rollback call"
> ER_PK_INDEX_CANT_BE_IGNORED
> eng "A primary key cannot be marked as IGNORE"
> +ER_FUNCTION_CANNOT_BE_USED_IN_CLAUSE
> + eng "Function '%s' cannot be used in the %s clause"
Is it the first function we've got that cannot be used in HAVING?
> diff --git a/sql/sql_derived.cc b/sql/sql_derived.cc
> index 35b4294707f..da6c567b87c 100644
> --- a/sql/sql_derived.cc
> +++ b/sql/sql_derived.cc
> @@ -656,14 +656,22 @@ static
> bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived)
> {
> SELECT_LEX_UNIT *unit= derived->get_unit();
> - bool res= FALSE;
> + SELECT_LEX *first_select;
> + bool res= FALSE, keep_row_order;
> DBUG_ENTER("mysql_derived_prepare");
> DBUG_PRINT("enter", ("unit: %p table_list: %p alias: '%s'",
> unit, derived, derived->alias.str));
> if (!unit)
> DBUG_RETURN(FALSE);
>
> - SELECT_LEX *first_select= unit->first_select();
> + first_select= unit->first_select();
> + /*
> + If rownum() is used we have to preserve the insert row order
> + to make group by with filesort to work.
it'd help if you'd add an example of a SELECT here
> + */
> + keep_row_order= (thd->lex->with_rownum &&
> + (first_select->group_list.elements ||
> + first_select->order_list.elements));
>
> if (derived->is_recursive_with_table() &&
> !derived->is_with_table_recursive_reference() &&
> diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
> index 806049b4465..5c4dff33914 100644
> --- a/sql/sql_insert.cc
> +++ b/sql/sql_insert.cc
> @@ -746,6 +746,9 @@ bool mysql_insert(THD *thd, TABLE_LIST *table_list,
> DBUG_RETURN(TRUE);
> }
> +
> + if (thd->lex->with_rownum && table_list->lock_type == TL_WRITE_DELAYED)
> + table_list->lock_type= TL_WRITE;
why? do you have a test case when it's needed?
>
> if (table_list->lock_type == TL_WRITE_DELAYED)
> {
> if (open_and_lock_for_insert_delayed(thd, table_list))
> @@ -968,11 +971,16 @@ bool mysql_insert(THD *thd, TABLE_LIST *table_list,
> */
> if (returning &&
> result->send_result_set_metadata(returning->item_list,
> - Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF))
> + Protocol::SEND_NUM_ROWS |
> + Protocol::SEND_EOF))
> goto values_loop_end;
>
> THD_STAGE_INFO(thd, stage_update);
> thd->decide_logging_format_low(table);
> + fix_rownum_pointers(thd, thd->lex->current_select, &info.copied);
> + if (returning)
> + fix_rownum_pointers(thd, thd->lex->returning(), &info.copied);
> +
Note that info.copied can be incremented more than once per row (in INSERT...ON
DUPLICATE KEY UPDATE, for example). This will probably break rownum logic.
> do
> {
> DBUG_PRINT("info", ("iteration %llu", iteration));
> @@ -2133,8 +2141,14 @@ int write_record(THD *thd, TABLE *table, COPY_INFO *info, select_result *sink)
> autoinc values (generated inside the handler::ha_write()) and
> values updated in ON DUPLICATE KEY UPDATE.
> */
> - if (sink && sink->send_data(thd->lex->returning()->item_list) < 0)
> - trg_error= 1;
> + if (sink)
> + {
> + /* We have to adjust 'copied' to make ROWNUM() work in RETURNING */
> + info->copied--;
> + if (sink->send_data(thd->lex->returning()->item_list) < 0)
> + trg_error= 1;
> + info->copied++;
this is quite silly. Can you simply increment info->copied after this
sink->send_data call?
> + }
>
> after_trg_or_ignored_err:
> if (key)
> diff --git a/sql/sql_limit.h b/sql/sql_limit.h
> index a4fcedac14a..62fd0546af0 100644
> --- a/sql/sql_limit.h
> +++ b/sql/sql_limit.h
> @@ -67,6 +67,15 @@ class Select_limit_counters
> { return select_limit_cnt; }
> ha_rows get_offset_limit()
> { return offset_limit_cnt; }
> +
> + void set_limit_if_lower(ha_rows limit)
> + {
> + if (!offset_limit_cnt)
I suppose, alternatively, you could've had
if (offset_limit_cnt + select_limit_cnt > limit)
select_limit_cnt= limit - offset_limit_cnt;
> + {
> + if (select_limit_cnt > limit)
> + select_limit_cnt= limit;
> + }
> + }
> };
>
> #endif // INCLUDES_MARIADB_SQL_LIMIT_H
> diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
> index 2bd2575b882..57ba9df42c0 100644
> --- a/sql/sql_yacc.yy
> +++ b/sql/sql_yacc.yy
> @@ -10286,6 +10287,22 @@ function_call_nonkeyword:
> if (unlikely($$ == NULL))
> MYSQL_YYABORT;
> }
> +/* Start SQL_MODE_ORACLE_SPECIFIC
> + | ROWNUM_SYM optional_braces
> + {
> + $$= new (thd->mem_root) Item_func_rownum(thd);
> + if (unlikely($$ == NULL))
> + MYSQL_YYABORT;
> + }
> +End SQL_MODE_ORACLE_SPECIFIC */
> +/* Start SQL_MODE_DEFAULT_SPECIFIC */
> + | ROWNUM_SYM '(' ')'
> + {
> + $$= new (thd->mem_root) Item_func_rownum(thd);
> + if (unlikely($$ == NULL))
> + MYSQL_YYABORT;
> + }
> +/* End SQL_MODE_DEFAULT_SPECIFIC */
You have two nearly identical rules compiled conditionally.
I can pretty much guarantee that they'll go out of sync eventually.
Better do something like
/* Start SQL_MODE_ORACLE_SPECIFIC
oracle_optional_braces: optional_braces ;
End SQL_MODE_ORACLE_SPECIFIC */
/* Start SQL_MODE_DEFAULT_SPECIFIC */
oracle_optional_braces: '(' ')' ;
/* End SQL_MODE_DEFAULT_SPECIFIC */
or even
| ROWNUM_SYM
/* Start SQL_MODE_ORACLE_SPECIFIC
optional_braces
End SQL_MODE_ORACLE_SPECIFIC */
/* Start SQL_MODE_DEFAULT_SPECIFIC */
'(' ')'
/* End SQL_MODE_DEFAULT_SPECIFIC */
{
$$= new (thd->mem_root) Item_func_rownum(thd);
if (unlikely($$ == NULL))
MYSQL_YYABORT;
}
> | SUBDATE_SYM '(' expr ',' expr ')'
> {
> $$= new (thd->mem_root) Item_date_add_interval(thd, $3, $5,
> diff --git a/sql/table.cc b/sql/table.cc
> index 7f3a6468aa2..100813e1f95 100644
> --- a/sql/table.cc
> +++ b/sql/table.cc
> @@ -9331,6 +9331,10 @@ bool TABLE_LIST::init_derived(THD *thd, bool init_view)
> {
> /* A subquery might be forced to be materialized due to a side-effect. */
> if (!is_materialized_derived() && first_select->is_mergeable() &&
> + (unit->outer_select() && !unit->outer_select()->with_rownum) &&
no merging if *outer select* uses rownum? why? example?
> + (!thd->lex->with_rownum ||
> + (!first_select->group_list.elements &&
> + !first_select->order_list.elements)) &&
no merging if no rownum but there's group by or order by?
group by - this is obvious, and is already checked earlier in this if()
order by - why?
> optimizer_flag(thd, OPTIMIZER_SWITCH_DERIVED_MERGE) &&
> !thd->lex->can_not_use_merged(1) &&
> !is_recursive_with_table())
> diff --git a/sql/sql_select.cc b/sql/sql_select.cc
> index 4bb0bc661bd..b002e27799b 100644
> --- a/sql/sql_select.cc
> +++ b/sql/sql_select.cc
> @@ -1789,10 +1803,18 @@ JOIN::optimize_inner()
> {
> DBUG_ENTER("JOIN::optimize_inner");
> subq_exit_fl= false;
> - do_send_rows = (unit->lim.get_select_limit()) ? 1 : 0;
>
> DEBUG_SYNC(thd, "before_join_optimize");
>
> + // rownum used somewhere in query, no limits and it is derived
> + if (unlikely(thd->lex->with_rownum &&
> + select_lex->first_cond_optimization &&
> + select_lex->master_unit()->derived))
> + optimize_upper_rownum_func();
> +
> + do_send_rows = (unit->lim.get_select_limit()) ? 1 : 0;
Is there any particular reason why you put that between
DEBUG_SYNC(thd, "before_join_optimize");
and
THD_STAGE_INFO(thd, stage_optimizing);
?
I'd expect them logically to go directly one after the other
> +
> +
> THD_STAGE_INFO(thd, stage_optimizing);
>
> set_allowed_join_cache_types();
> @@ -14210,7 +14236,24 @@ static ORDER *
> remove_const(JOIN *join,ORDER *first_order, COND *cond,
> bool change_list, bool *simple_order)
> {
> - *simple_order= join->rollup.state == ROLLUP::STATE_NONE;
> + /*
> + We can't do ORDER BY using filesort if the select list contains a non
> + deterministic value like RAND() or ROWNUM().
> + For example:
> + SELECT RAND() as 'r' from t1 order by r;
This one uses temporary for me. Can you put here a correct example please?
> +
> + If we would first sort the table 't1', the RAND() column would be generated
> + during end_send() and the order would be wrong.
> +
> + Previously we had here also a test of ROLLUP:
> + 'join->rollup.state == ROLLUP::STATE_NONE'
> + I deleted this because
> + the ROLLUP was never enforced because of a bug where the inital value
> + of simple_order was ignored. Having ROLLUP tested now when the code
> + is fixed causes many test failure and some wrong results so better to
> + leave the code as it was related to ROLLUP.
No need to explain in a comment why something that is no longer here was removed.
Use git for that, commit comments. The code comment should explain the code as it is.
> + */
> + *simple_order= !join->rand_table_in_field_list;
why do you need rand_table_in_field_list instead of writing
*simple_order= join->select_lex->select_list_tables & RAND_TABLE_BIT;
?
> if (join->only_const_tables())
> return change_list ? 0 : first_order; // No need to sort
>
> @@ -29587,6 +29640,273 @@ void unpack_to_base_table_fields(TABLE *table)
> (*cp->do_copy)(cp);
> }
>
> +/*
> + Call item->fix_after_optimize for all items registered in
> + lex->fix_after_optimize
> +
> + This is needed for items like ROWNUM(), which needs access to structures
> + created by the early optimizer pass, like JOIN
> +*/
> +
> +static void fix_items_after_optimize(THD *thd, SELECT_LEX *select_lex)
> +{
> + List_iterator<Item> li(select_lex->fix_after_optimize);
> +
> + while (Item *item= li++)
> + item->fix_after_optimize(thd);
> +}
> +
> +
here you could've had a comment, like
/* callbacks for process_direct_rownum_comparison() */
> +static bool is_const(Item *item)
> +{
> + /*
> + Constant expression in WHERE can be also subquery or other expensive
> + thing we shoud not evaluate on OPTIMIZATION phase
> + */
> + return item->const_item() && !item->is_expensive();
> +}
> +
> +
> +// Check if this is an unexpensive functional expression over basic constants
> +
> +static bool is_basic_const(Item *item)
> +{
> + if (item->basic_const_item())
> + return true;
> + if (!item->const_item() || item->is_expensive())
> + return false;
> + if (item->type() == Item::FUNC_ITEM)
> + {
> + Item_func *func= ((Item_func *)item);
> + if (func->argument_count() == 0)
> + return false;
> + bool result= true;
> + Item **args= func->arguments();
> + for (uint i= 0; i < func->argument_count() && result; i++)
> + result= result && is_basic_const(args[i]);
> + return result;
> + }
> + return false;
> +}
is_basic_const() is a misleading name, a function of basic consts isn't
a basic const itself.
what's an example of an expression has is_const() == true, but
is_basic_const() == false?
> +
> +
> +inline bool is_simple_rownum_exp(Item *rownum, Item *constant)
unused
> +{
> + return (constant->basic_const_item() &&
> + rownum->type() == Item::FUNC_ITEM &&
> + ((Item_func*) rownum)->functype() == Item_func::ROWNUM_FUNC);
> +}
> +
> +
> +static bool temporary_set_limit(THD *thd __attribute__((unused)),
> + SELECT_LEX_UNIT *unit,
> + ha_rows lim)
> +{
> + unit->set_limit_if_lower(lim);
why is it temporary?
in the PS/SP sense, just for one execution?
> + return false;
> +}
> +
> +
> +static bool permanent_limit(THD *thd, SELECT_LEX_UNIT *unit, ha_rows lim)
> +{
> + SELECT_LEX *gpar= unit->global_parameters();
> + if (gpar->select_limit != 0 &&
> + // limit can not be an expression but can be parameter
> + (!gpar->select_limit->basic_const_item() ||
> + ((ha_rows)gpar->select_limit->val_int()) < lim))
> + return false;
> +
> + Query_arena *arena, backup;
> + arena= thd->activate_stmt_arena_if_needed(&backup);
> +
> + gpar->select_limit=
> + new (thd->mem_root)Item_int(thd, lim, 20 /* max 64 bit length*/ );
we have defines for that, MAX_BIGINT_WIDTH, MY_INT64_NUM_DECIMAL_DIGITS,
LONGLONG_BUFFER_SIZE - whatever you prefer.
> + if (gpar->select_limit == 0)
> + return true; // EOM
> +
> + unit->set_limit(gpar);
> +
> + gpar->explicit_limit= true; // to show in EXPLAIN
> +
> + if (arena)
> + thd->restore_active_arena(arena, &backup);
> +
> + return false;
> +}
> +
> +
> +/**
> + Check posibility of LIMIT setting by rownum() of upper SELECT and do it
> +
> + @note Ideal is to convert something like
> + SELECT ...
> + FROM (SELECT ...) table
> + WHERE rownum() < <CONSTANT>;
> + to
> + SELECT ...
> + FROM (SELECT ... LIMIT <CONSTANT>) table
> + WHERE rownum() < <CONSTANT>;
1. what if the outer select uses LIMIT, not ROWNUM?
why not to push that down too?
2. why are you not removing rownum from the outer select?
if you remove rownum and reset with_rownum=false, it'll generally
give optimizer more freedom.
> +
> + @retval true EOM
> + @retval false no errors
> +*/
> +
> +bool JOIN::optimize_upper_rownum_func()
> +{
> + DBUG_ASSERT(select_lex->master_unit()->derived);
> +
> + if (select_lex->master_unit()->first_select() != select_lex)
> + return false; // first will set parameter
> +
> + if (select_lex->master_unit()->global_parameters()->offset_limit != NULL)
> + return false; // offset is set, we cannot set limit
> +
> + SELECT_LEX *outer_select= select_lex->master_unit()->outer_select();
> + /*
> + Check that the outer query (the one that has 'WHERE rownum()...') is using
> + to see if the can be use it to limit this sub query
> + */
> + if (outer_select == NULL ||
> + !outer_select->with_rownum ||
> + (outer_select->options & SELECT_DISTINCT) ||
> + outer_select->table_list.elements != 1 ||
> + outer_select->where == NULL ||
> + outer_select->where->type() != Item::FUNC_ITEM)
> + return false;
> +
> + return process_direct_rownum_comparison(thd, unit, outer_select->where,
> + &is_basic_const,
> + &permanent_limit);
> +}
> +
> +/**
> + Test if the predicate compares rownum() with a constant
> +
> + @return 1 No or invalid rownum() compare
> + @return 0 rownum() is compared with a constant.
> + In this case *args contains the constant and
> + *inv_order constains 1 if the rownum() was the right
> + argument, like in 'WHERE 2 >= rownum()'.
> +*/
> +
> +static bool check_rownum_usage(Item_func *func_item, longlong *limit,
> + bool *inv_order, const_probe probe)
> +{
> + Item *arg1, *arg2;
> + *inv_order= 0;
> + DBUG_ASSERT(func_item->argument_count() == 2);
> +
> + /* 'rownum op const' or 'const op field' */
> + arg1= func_item->arguments()[0]->real_item();
> + if (arg1->type() == Item::FUNC_ITEM &&
> + ((Item_func*) arg1)->functype() == Item_func::ROWNUM_FUNC)
> + {
> + arg2= func_item->arguments()[1]->real_item();
> + if ((*probe)(arg2))
> + {
> + *limit= arg2->val_int();
> + return *limit <= 0 || (ulonglong) *limit >= HA_POS_ERROR;
> + }
> + }
> + else if ((*probe)(arg1))
> + {
> + arg2= func_item->arguments()[1]->real_item();
why not to assign arg2 outside of the if() ?
> + if (arg2->type() == Item::FUNC_ITEM &&
> + ((Item_func*) arg2)->functype() == Item_func::ROWNUM_FUNC)
> + {
> + *limit= arg1->val_int();
> + *inv_order= 1;
> + return *limit <= 0 || (ulonglong) *limit >= HA_POS_ERROR;
> + }
> + }
> + return 1;
> +}
> +
> +
> +/*
> + Limit optimization for ROWNUM()
> +
> + Go through the WHERE clause and find out if there are any of the following
> + constructs on the top level:
> + rownum() <= integer_constant
> + rownum() < integer_constant
> + rownum() = 1
> +
> + If yes, then threat the select as if 'LIMIT integer_constant' would
> + have been used
> +*/
> +
> +static void optimize_rownum(THD *thd, SELECT_LEX_UNIT *unit, Item *cond)
> +{
> + DBUG_ENTER("optimize_rownum");
> +
> + if (cond->type() == Item::COND_ITEM)
> + {
> + if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC)
> + {
> + List_iterator<Item> li(*((Item_cond*) cond)->argument_list());
> + Item *item;
> + while ((item= li++))
> + optimize_rownum(thd, unit, item);
> + }
> + DBUG_VOID_RETURN;
> + }
> +
> + process_direct_rownum_comparison(thd, unit, cond, &is_const,
> + &temporary_set_limit);
please, explain why it's is_const/temporary_set_limit here and
is_basic_const/permanent_limit in optimize_upper_rownum_func().
> + DBUG_VOID_RETURN;
> +}
> +
> +
> +static bool process_direct_rownum_comparison(THD *thd,
> + SELECT_LEX_UNIT *unit,
> + Item *cond,
> + const_probe probe,
> + set_limit_callback set_limit)
> +{
> + DBUG_ENTER("process_direct_rownum_comparison");
> + if (cond->real_type() == Item::FUNC_ITEM)
> + {
> + Item_func *pred= (Item_func*) cond;
> + longlong limit;
> + bool inv;
> +
> + if (pred->argument_count() != 2)
> + DBUG_RETURN(false); // Not a compare functions
> + if (check_rownum_usage(pred, &limit, &inv, probe))
> + DBUG_RETURN(false);
> +
> + Item_func::Functype pred_type= pred->functype();
> +
> + if (inv && pred_type != Item_func::EQ_FUNC)
> + {
> + if (pred_type == Item_func::GT_FUNC) // # > rownum()
> + pred_type= Item_func::LT_FUNC;
> + else if (pred_type == Item_func::GE_FUNC) // # >= rownum()
> + pred_type= Item_func::LE_FUNC;
> + else
> + DBUG_RETURN(false);
> + }
> + switch (pred_type) {
> + case Item_func::LT_FUNC: // rownum() < #
> + {
> + if (limit <= 0)
> + DBUG_RETURN(false);
> + DBUG_RETURN((*set_limit)(thd, unit, limit - 1));
> + case Item_func::LE_FUNC:
> + DBUG_RETURN((*set_limit)(thd, unit, limit));
> + case Item_func::EQ_FUNC:
> + if (limit == 1)
> + DBUG_RETURN((*set_limit)(thd, unit, limit));
> + break;
> + default:
> + break;
> + }
> + }
what if it's rownum() > 5 ?
why not to mark it as always false right away?
> + }
> + DBUG_RETURN(false);
> +}
> +
>
> /**
> @} (end of group Query_Optimizer)
Regards,
Sergei
VP of MariaDB Server Engineering
and security@xxxxxxxxxxx
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