maria-discuss team mailing list archive

[Federico Razzoli <federico_raz@xxxxxxxx>]

Hello list

I found out that EXPLAIN SELECT aggregate_func() FROM connect_table returns a "rows" value which is much greater than the rows in the table. For example:

MariaDB [test]> SELECT COUNT(*) FROM t;
+----------+
| COUNT(*) |
+----------+
|  1000000 |
+----------+
1 row in set (0.49 sec)

MariaDB [test]> EXPLAIN SELECT COUNT(*) FROM t;
+------+-------------+-------+------+---------------+------+---------+------+---------+-------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows    | Extra |
+------+-------------+-------+------+---------------+------+---------+------+---------+-------+
|    1 | SIMPLE      | t     | ALL  | NULL          | NULL | NULL    | NULL | 7783705 |       |
+------+-------------+-------+------+---------------+------+---------+------+---------+-------+

So, my question is: is there any difference in the output of EXPLAIN with CONNECT? Is CONNECT really reading 7.8 millions rows in a table with only 1 million rows?

Regards
Federico