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Taxonomy: Improve AND term query performance #12535

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Taxonomy: Improve AND term query performance #12535

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7ba5930
Taxonomy: Improve AND term query performance
Sukhendu2002 Jul 15, 2026
e451b9e
Merge branch 'trunk' into perf/16706-tax-query-and-join
Sukhendu2002 Jul 15, 2026
c1b0a13
Merge branch 'trunk' into perf/16706-tax-query-and-join
Sukhendu2002 Aug 10, 2026
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23 changes: 23 additions & 0 deletions src/wp-includes/class-wp-tax-query.php
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Original file line number Diff line number Diff line change
Expand Up @@ -451,6 +451,29 @@ public function get_sql_for_clause( &$clause, $parent_query ) {
return $sql;
}

/*
* Individual joins avoid a correlated subquery for small term intersections.
* Limit total taxonomy joins to three because additional joins can cost more
* than the subquery for common terms.
*/
if ( 3 >= count( $terms ) + count( $this->table_aliases ) ) {
foreach ( $terms as $term ) {
$i = count( $this->table_aliases );
$alias = $i ? 'tt' . $i : $wpdb->term_relationships;

$this->table_aliases[] = $alias;

$join = " LEFT JOIN $wpdb->term_relationships";
$join .= $i ? " AS $alias" : '';
$join .= " ON ($this->primary_table.$this->primary_id_column = $alias.object_id)";

$sql['join'][] = $join;
$sql['where'][] = "$alias.term_taxonomy_id IN ($term)";
}

return $sql;
}

$num_terms = count( $terms );

$terms = implode( ',', $terms );
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94 changes: 94 additions & 0 deletions tests/phpunit/tests/term/taxQuery.php
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Original file line number Diff line number Diff line change
Expand Up @@ -505,6 +505,100 @@ public function test_get_sql_operator_and_empty_terms() {
_unregister_taxonomy( 'wptests_tax' );
}

/**
* @ticket 16706
*/
public function test_get_sql_operator_and_uses_joins_for_three_or_fewer_terms() {
$tq = new WP_Tax_Query(
array(
array(
'field' => 'term_taxonomy_id',
'operator' => 'AND',
'terms' => range( 1, 3 ),
),
)
);

global $wpdb;
$sql = $tq->get_sql( $wpdb->posts, 'ID' );

$this->assertSame( 3, substr_count( $sql['join'], 'JOIN' ) );
$this->assertStringNotContainsString( 'SELECT COUNT(1)', $sql['where'] );
}

/**
* @ticket 16706
*/
public function test_get_sql_operator_and_uses_subquery_for_more_than_three_terms() {
$tq = new WP_Tax_Query(
array(
array(
'field' => 'term_taxonomy_id',
'operator' => 'AND',
'terms' => range( 1, 4 ),
),
)
);

global $wpdb;
$sql = $tq->get_sql( $wpdb->posts, 'ID' );

$this->assertSame( '', $sql['join'] );
$this->assertStringContainsString( 'SELECT COUNT(1)', $sql['where'] );
}

/**
* @ticket 16706
*/
public function test_get_sql_operator_and_limits_total_joins_across_clauses() {
$tq = new WP_Tax_Query(
array(
array(
'field' => 'term_taxonomy_id',
'operator' => 'AND',
'terms' => range( 1, 2 ),
),
array(
'field' => 'term_taxonomy_id',
'operator' => 'AND',
'terms' => range( 3, 4 ),
),
)
);

global $wpdb;
$sql = $tq->get_sql( $wpdb->posts, 'ID' );

$this->assertSame( 2, substr_count( $sql['join'], 'JOIN' ) );
$this->assertStringContainsString( 'SELECT COUNT(1)', $sql['where'] );
}

/**
* @ticket 16706
*/
public function test_get_sql_operator_and_counts_existing_in_join_toward_limit() {
$tq = new WP_Tax_Query(
array(
array(
'field' => 'term_taxonomy_id',
'operator' => 'IN',
'terms' => 1,
),
array(
'field' => 'term_taxonomy_id',
'operator' => 'AND',
'terms' => range( 2, 4 ),
),
)
);

global $wpdb;
$sql = $tq->get_sql( $wpdb->posts, 'ID' );

$this->assertSame( 1, substr_count( $sql['join'], 'JOIN' ) );
$this->assertStringContainsString( 'SELECT COUNT(1)', $sql['where'] );
}

/**
* @ticket 18105
* @covers WP_Tax_Query::get_sql
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