( [resource link_identifier] )
mssql_close() closes the link to a MS SQL
Server database that's associated with the specified link
identifier. If the link identifier isn't specified, the last
opened link is assumed.
如果成功则返回 TRUE，失败则返回 FALSE。
Note that this isn't usually necessary, as non-persistent open
links are automatically closed at the end of the script's
mssql_close() will not close persistent links
generated by mssql_pconnect().