mysql and indexes with more than one column

Posted by clarkk on Stack Overflow See other posts from Stack Overflow or by clarkk
Published on 2012-11-10T10:43:48Z Indexed on 2012/11/10 11:00 UTC
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mysql

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database-indexes

How to use indexes with more than one column

The original index has an index on block_id, but is it necesarry when it's already in the unique index with two column?

Indexes with more than one column

(a,b,c)

you can search for a, b and c
you can search for a and b
you can search for a
you can not search for a and c

Does this apply to unique indexes too?

table

id
block_id
account_id
name

indexes origin

PRIMARY KEY (`id`)
UNIQUE KEY `block_id` (`block_id`,`account_id`)
KEY `block_id` (`block_id`),
KEY `account_id` (`account_id`),

indexes alternative

PRIMARY KEY (`id`)
UNIQUE KEY `block_id` (`block_id`,`account_id`)
KEY `account_id` (`account_id`),

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