maria-discuss team mailing list archive

[Federico Razzoli <federico_raz@xxxxxxxx>]

That's a strange index. In InnoDB, tables are organized by primary key, so ALL indexes contain primary keys values.

In other storage engines... well, I can't think a use case when that index would make sense. Maybe a more realistic example would help :)

Federico


--------------------------------------------
Mar 23/6/15, Roberto Spadim <roberto@xxxxxxxxxxxxx> ha scritto:

 Oggetto: Re: [Maria-discuss] doubt about index
 A: "Reindl Harald" <h.reindl@xxxxxxxxxxxxx>
 Cc: "Maria Discuss" <maria-discuss@xxxxxxxxxxxxxxxxxxx>
 Data: Martedì 23 giugno 2015, 00:53
 
 2015-06-22 19:47 GMT-03:00
 Reindl Harald <h.reindl@xxxxxxxxxxxxx>:
 
 
 
 
 Am 23.06.2015 um 00:43 schrieb Roberto Spadim:
 
 
 hi guys, i`m with a doubt...
 
 when i have a primary key i know that's a unique key
 
 when i have a index with primary key + any other column,
 does mariadb
 
 consider that it's unique too?
 
 
 
 
 if it is defined as unique key yes
 
 
 
 what is "index with primary key + any other
 column"?
 
 for examplecreate table
 x(i int, b int,c int, d
 int , e int, ... primary key(i),key
 teste(b,i))
 the test index is primary key (i
 column) + any other column (b,c,d,e,...)
 
  
 you have two keys in that case and the select uses one of
 themyeap but some search algorithms use
 unique key/non unique key information to improve search
 right? does it consider that any index that
 contains a unique index columns + anyother column as
 "unique"  
 
 
 
 
 i`m thinking more about SELECT optimization
 
 
 
 
 how does it matter if a key is unique or not for select
 optimization?
 
 select "where i=1" should
 return 0/1 rows (it's unique), 
 "where b=1" should return 0+ rows,
 but "where b=1 and i=1" should return 0/1
 rows
 
 
 -- 
 Roberto Spadim
 SPAEmpresarial - Software ERPEng.
 Automação e Controle
 
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