[wp-trac] [WordPress Trac] #24093: WP_Meta_Query is inefficient when referencing the same keys in "OR" query

[WordPress Trac]

#24093: WP_Meta_Query is inefficient when referencing the same keys in "OR" query
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 Reporter:  sc0ttkclark           |       Owner:  boonebgorges
     Type:  defect (bug)          |      Status:  accepted
 Priority:  normal                |   Milestone:  4.1
Component:  Query                 |     Version:  3.5.1
 Severity:  normal                |  Resolution:
 Keywords:  meta-query has-patch  |     Focuses:  performance
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Comment (by boonebgorges):

 In [changeset:"29940"]:
 {{{
 #!CommitTicketReference repository="" revision="29940"
 Overhaul SQL generating logic in WP_Meta_Query to avoid unnecessary table
 joins.

 The logic used to generate clause SQL in `WP_Meta_Query` is somewhat
 arcane,
 stemming mostly from an ongoing effort to eliminate costly table joins
 when
 they are not necessary. By systematizing the process of looking for
 shareable
 joins - as was done in `WP_Tax_Query` [29902] - it becomes possible to
 simplify
 the construction of SQL queries in `get_sql_for_clause()`. Moreover, the
 simplified logic is actually considerably better at identifying shareable
 joins, such that certain uses of `WP_Meta_Query` will see joins reduced by
 50%
 or more.

 Includes integration tests for a representative cross-section of the query
 clause combinations that result in shared table aliases.

 Props boonebgorges, sc0ttkclark.
 See #24093.
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/24093#comment:37>
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