MSSQL Try Catch Rollback and Conditional RETURN - sql

Question

SET XACT_ABORT ON
BEGIN TRY
BEGIN TRANSACTION
UPDATE [Members] SET [Count] = [Count] - 1 WHERE [Count] > 0;
**return 0 here if this statement updated 0 rows**
INSERT INTO [Sessions] ([Name], [Etc]) VALUES ('Test', 'Other')
COMMIT TRANSACTION
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0
ROLLBACK TRANSACTION;
RETURN 0
END CATCH
SELECT SCOPE_IDENTITY(); **only return the identity if the first statement updated 1 row and no exceptions occurred.**
With the code above, is there a way to return 0 if the first UPDATE updated no rows? I only want the INDENTITY() if the first UPDATE edits a row and no errors occur. Is this possible?

Answer 1

You can use ##ROWCOUNT to get the number changed. This should work:
UPDATE [Members] SET [Count] = [Count] - 1 WHERE [Count] > 0;
IF ##ROWCOUNT = 0
BEGIN
COMMIT TRANSACTION;
RETURN;
END;
Because no rows are updated, I suppose rolling back the transaction would be equivalent.
To get the identify values inserted, I would recommend that you learn to use the OUTPUT clause in INSERT (documented here). This is a good habit to get into, although the syntax is a bit more cumbersome (you have to define a table/table variable to store the inserted values). It has no race conditions and it allows you return multiple identity values.

Answer 2

Only read SCOPE_IDENTITY if you actually INSERT
This way, you have one exit point only
BEGIN TRY
BEGIN TRANSACTION
UPDATE [Members] SET [Count] = [Count] - 1 WHERE [Count] > 0;
IF ##ROWCOUNT = 1
BEGIN
INSERT INTO [Sessions] ([Name], [Etc]) VALUES ('Test', 'Other')
SET #rtn = SCOPE_IDENTITY();
END
SET #rtn = 0;
COMMIT TRANSACTION;
SELECT #rtn
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0 ROLLBACK TRANSACTION;
END CATCH