msql_close() closes the non-persistent connection to the mSQL server that's associated with the specified link identifier.
Using msql_close() isn't usually necessary, as non-persistent open links are automatically closed at the end of the script's execution. See also freeing resources.
mSQL 的连接。如果没有指定，默认使用最后被 msql_connect() 打开的连接。如果没有找到该连接，函数会尝试通过调用已定义的 msql_connect() 重新建立连接并使用它。