db\mssql\SqlsrvPDO lastInsertId()

Returns value of the last inserted ID.

SQLSRV driver implements yii\db\mssql\PDO::lastInsertId() method but with a single peculiarity: when $sequence value is a null or an empty string it returns an empty string. But when parameter is not specified it works as expected and returns actual last inserted ID (like the other PDO drivers).