This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0.
Instead, the MySQLi or PDO_MySQL extension should be used.
See also MySQL: choosing an API guide.
Alternatives to this function include:
Retrieves the current thread ID. If the connection is lost, and a reconnect
with mysql_ping() is executed, the thread ID will
change. This means only retrieve the thread ID when needed.
Parameters
link_identifier
The MySQL connection. If the
link identifier is not specified, the last link opened by
mysql_connect() is assumed. If no such link is found, it
will try to create one as if mysql_connect() had been called
with no arguments. If no connection is found or established, an
E_WARNING level error is generated.