Note that when migrating your MS SQL Server PHP Driver from MSSQL to SQLSRV, if you have used mssql_num_rows, replacing them with sqlsrv_num_rows and replacing mssql_query($query, $mssql_link) with sqlsrv_query($sqlsrv_link, $query) calls will make your sqlsrv_num_rows calls fail. In order to avoid that, you should specify either static, keyset or buffered cursors (buffered cursor has been available since SQLSRV 3.0) when calling sqlsrv_query. For example,
sqlsrv_query($sqlsrv_link, $query, array(), array('Scrollable' => 'buffered'));
Using the buffered cursor is "more equivalent" than using the static or keyset cursors to simple mssql_query calls, since it caches the entire result set in client memory.