Source

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

protected function parse_orderby_meta( $orderby_raw ) {
		$orderby = '';

		// Tell the meta query to generate its SQL, so we have access to table aliases.
		$this->meta_query->get_sql( 'term', 't', 'term_id' );
		$meta_clauses = $this->meta_query->get_clauses();
		if ( ! $meta_clauses || ! $orderby_raw ) {
			return $orderby;
		}

		$allowed_keys       = array();
		$primary_meta_key   = null;
		$primary_meta_query = reset( $meta_clauses );
		if ( ! empty( $primary_meta_query['key'] ) ) {
			$primary_meta_key = $primary_meta_query['key'];
			$allowed_keys[]   = $primary_meta_key;
		}
		$allowed_keys[] = 'meta_value';
		$allowed_keys[] = 'meta_value_num';
		$allowed_keys   = array_merge( $allowed_keys, array_keys( $meta_clauses ) );

		if ( ! in_array( $orderby_raw, $allowed_keys, true ) ) {
			return $orderby;
		}

		switch ( $orderby_raw ) {
			case $primary_meta_key:
			case 'meta_value':
				if ( ! empty( $primary_meta_query['type'] ) ) {
					$orderby = "CAST({$primary_meta_query['alias']}.meta_value AS {$primary_meta_query['cast']})";
				} else {
					$orderby = "{$primary_meta_query['alias']}.meta_value";
				}
				break;

			case 'meta_value_num':
				$orderby = "{$primary_meta_query['alias']}.meta_value+0";
				break;

			default:
				if ( array_key_exists( $orderby_raw, $meta_clauses ) ) {
					// $orderby corresponds to a meta_query clause.
					$meta_clause = $meta_clauses[ $orderby_raw ];
					$orderby     = "CAST({$meta_clause['alias']}.meta_value AS {$meta_clause['cast']})";
				}
				break;
		}

		return $orderby;
	}