WP_Tax_Query::get_sql_for_clause( array $clause, array $parent_query ): array

384	public function get_sql_for_clause( &$clause, $parent_query ) {385		global $wpdb;386 387		$sql = array(388			'where' => array(),389			'join'  => array(),390		);391 392		$join  = '';393		$where = '';394 395		$this->clean_query( $clause );396 397		if ( is_wp_error( $clause ) ) {398			return self::$no_results;399		}400 401		$terms    = $clause['terms'];402		$operator = strtoupper( $clause['operator'] );403 404		if ( 'IN' === $operator ) {405 406			if ( empty( $terms ) ) {407				return self::$no_results;408			}409 410			$terms = implode( ',', $terms );411 412			/*413			 * Before creating another table join, see if this clause has a414			 * sibling with an existing join that can be shared.415			 */416			$alias = $this->find_compatible_table_alias( $clause, $parent_query );417			if ( false === $alias ) {418				$i     = count( $this->table_aliases );419				$alias = $i ? 'tt' . $i : $wpdb->term_relationships;420 421				// Store the alias as part of a flat array to build future iterators.422				$this->table_aliases[] = $alias;423 424				// Store the alias with this clause, so later siblings can use it.425				$clause['alias'] = $alias;426 427				$join .= " LEFT JOIN $wpdb->term_relationships";428				$join .= $i ? " AS $alias" : '';429				$join .= " ON ($this->primary_table.$this->primary_id_column = $alias.object_id)";430			}431 432			$where = "$alias.term_taxonomy_id $operator ($terms)";433 434		} elseif ( 'NOT IN' === $operator ) {435 436			if ( empty( $terms ) ) {437				return $sql;438			}439 440			$terms = implode( ',', $terms );441 442			$where = "$this->primary_table.$this->primary_id_column NOT IN (443				SELECT object_id444				FROM $wpdb->term_relationships445				WHERE term_taxonomy_id IN ($terms)446			)";447 448		} elseif ( 'AND' === $operator ) {449 450			if ( empty( $terms ) ) {451				return $sql;452			}453 454			$num_terms = count( $terms );455 456			$terms = implode( ',', $terms );457 458			$where = "(459				SELECT COUNT(1)460				FROM $wpdb->term_relationships461				WHERE term_taxonomy_id IN ($terms)462				AND object_id = $this->primary_table.$this->primary_id_column463			) = $num_terms";