Summery Summery

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

Syntax Syntax

WP_Tax_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_Tax_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|false) Table alias if found, otherwise false.

Source Source

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

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

		// Sanity check. Only IN queries use the JOIN syntax.
		if ( ! isset( $clause['operator'] ) || 'IN' !== $clause['operator'] ) {
			return $alias;

		// Since we're only checking IN queries, we're only concerned with OR relations.
		if ( ! isset( $parent_query['relation'] ) || 'OR' !== $parent_query['relation'] ) {
			return $alias;

		$compatible_operators = array( 'IN' );

		foreach ( $parent_query as $sibling ) {
			if ( ! is_array( $sibling ) || ! $this->is_first_order_clause( $sibling ) ) {

			if ( empty( $sibling['alias'] ) || empty( $sibling['operator'] ) ) {

			// The sibling must both have compatible operator to share its alias.
			if ( in_array( strtoupper( $sibling['operator'] ), $compatible_operators, true ) ) {
				$alias = $sibling['alias'];

		return $alias;


Changelog Changelog

Version Description
4.1.0 Introduced.


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