Summery Summery

Identify an existing table alias that is compatible with the current query clause.

Syntax Syntax

WP_Meta_Query::find_compatible_table_alias( array $clause, array $parent_query )

Description Description

We avoid unnecessary table joins by allowing each clause to look for an existing table alias that is compatible with the query that it needs to perform.

An existing alias is compatible if (a) it is a sibling of $clause (ie, it’s under the scope of the same relation), and (b) the combination of operator and relation between the clauses allows for a shared table join. In the case of WP_Meta_Query, this only applies to ‘IN’ clauses that are connected by the relation ‘OR’.

Parameters Parameters


(Required) Query clause.


(Required) Parent query of $clause.

Return Return

(string|bool) Table alias if found, otherwise false.

Source Source

File: wp-includes/class-wp-meta-query.php

	protected function find_compatible_table_alias( $clause, $parent_query ) {
		$alias = false;

		foreach ( $parent_query as $sibling ) {
			// If the sibling has no alias yet, there's nothing to check.
			if ( empty( $sibling['alias'] ) ) {

			// We're only interested in siblings that are first-order clauses.
			if ( ! is_array( $sibling ) || ! $this->is_first_order_clause( $sibling ) ) {

			$compatible_compares = array();

			// Clauses connected by OR can share joins as long as they have "positive" operators.
			if ( 'OR' === $parent_query['relation'] ) {
				$compatible_compares = array( '=', 'IN', 'BETWEEN', 'LIKE', 'REGEXP', 'RLIKE', '>', '>=', '<', '<=' );

				// Clauses joined by AND with "negative" operators share a join only if they also share a key.
			} elseif ( isset( $sibling['key'] ) && isset( $clause['key'] ) && $sibling['key'] === $clause['key'] ) {
				$compatible_compares = array( '!=', 'NOT IN', 'NOT LIKE' );

			$clause_compare  = strtoupper( $clause['compare'] );
			$sibling_compare = strtoupper( $sibling['compare'] );
			if ( in_array( $clause_compare, $compatible_compares, true ) && in_array( $sibling_compare, $compatible_compares, true ) ) {
				$alias = $sibling['alias'];

		 * Filters the table alias identified as compatible with the current clause.
		 * @since 4.1.0
		 * @param string|bool   $alias        Table alias, or false if none was found.
		 * @param array         $clause       First-order query clause.
		 * @param array         $parent_query Parent of $clause.
		 * @param WP_Meta_Query $this         WP_Meta_Query object.
		return apply_filters( 'meta_query_find_compatible_table_alias', $alias, $clause, $parent_query, $this );


Changelog Changelog

Version Description
4.1.0 Introduced.


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