MySQL Forums
Forum List  »  Performance

Re: index not being pick up
Posted by: Peter Brawley
Date: January 17, 2018 12:41PM

Given tables a, b with matchable indexed id columns, Explain will tell you that the query engine will not use an index on table a in the query ...

select a.* from a join b using(id);

... because it sees that the query requires the engine to read all the data in table a, so an index on it won't help performance.

But it will use an index for ...

select b.* from a join b using(id);

... because now the index offers an advantage.

Options: ReplyQuote


Subject
Views
Written By
Posted
249
r r
January 15, 2018 11:57PM
114
January 16, 2018 12:19AM
106
January 16, 2018 04:39PM
110
January 16, 2018 07:49PM
112
January 17, 2018 12:26AM
118
January 17, 2018 01:07AM
153
January 17, 2018 01:19AM
Re: index not being pick up
130
January 17, 2018 12:41PM
107
January 19, 2018 07:26AM
124
January 21, 2018 04:31PM
99
January 21, 2018 05:41PM
109
January 22, 2018 03:00AM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.