1708a580fd
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. git-svn-id: https://develop.svn.wordpress.org/trunk@29940 602fd350-edb4-49c9-b593-d223f7449a82