Source

File: wp-includes/wp-db.php

public function check_database_version() {
		global $wp_version, $required_mysql_version;
		// Make sure the server has the required MySQL version.
		if ( version_compare( $this->db_version(), $required_mysql_version, '<' ) ) {
			/* translators: 1: WordPress version number, 2: Minimum required MySQL version number. */
			return new WP_Error( 'database_version', sprintf( __( '<strong>Error</strong>: WordPress %1$s requires MySQL %2$s or higher' ), $wp_version, $required_mysql_version ) );
		}
	}