fbsql_select_db() sets the current active database on the server that's associated with the specified link identifier. If no link identifier is specified, the last opened link is assumed. If no link is open, the function will try to establish a link as if fbsql_connect() was called, and use it.
如果成功则返回 TRUE，失败则返回 FALSE。
The client contacts FBExec to obtain the port number to use for the connection to the database. If the database name is a number the system will use that as a port number and it will not ask FBExec for the port number. The FrontBase server can be stared as FRontBase -FBExec=No -port=<port number> <database name>.
Every subsequent call to fbsql_query() will be made on the active database.
if the database is protected with a database password, the user must call fbsql_database_password() before selecting the database.
See also fbsql_connect(), fbsql_pconnect(), fbsql_database_password(), and fbsql_query().