[wp-trac] [WordPress Trac] #36670: Move CAST to right-hand side of comparison in meta query

[WordPress Trac]

#36670: Move CAST to right-hand side of comparison in meta query
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 Reporter:  ericlewis    |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  Awaiting Review
Component:  Query        |    Version:  3.1
 Severity:  normal       |   Keywords:
  Focuses:               |
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 The SQL clause created by a meta query
 [https://github.com/WordPress/WordPress/blob/4.5/wp-includes/class-wp-
 meta-query.php#L634 CASTs the column value] `postmeta.meta_value` and
 compares it to the value provided in the meta query, a la
 `CAST(postmeta.meta_value AS CHAR) = 'some-value'`.

 Casting a column value instead of a constant means that MySQL will ignore
 an index for that column if one exists. Although core does not define an
 index for the `meta_value` column, a user could create one for perf
 reasons.

 Switching the side of the CAST would result in the same two types, just on
 different sides

 `postmeta.meta_value = CAST('some-value' AS CHAR)`

 That means [http://dev.mysql.com/doc/refman/5.7/en/type-conversion.html
 MySQL's type conversion] will work the same as it did previously.

 #36649 would need to be completed before this.

 Related: #27272, #36625

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Ticket URL: <https://core.trac.wordpress.org/ticket/36670>
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