msql_select_db() sets the current active database on
the server that's associated with the specified
link_identifier
.
Subsequent calls to msql_query() will be made on the active database.
database_name
The database name.
link_identifier
mSQL 的连接标识符。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 msql_connect() 建立连接并使用它。