SQL Server stored procedure return code oddity

问题:

The client that calls this code is restricted and can only deal with return codes from stored procs. So, we modified our usual contract to RETURN -1 on error and default to RETURN 0 if no error

If the code hits the inner catch block, then the RETURN code default is -4 rather then 0

Does anyone know where this comes from please? With reference

Cheers gbn

IF OBJECT_ID('dbo.foo') IS NOT NULL DROP TABLE dbo.foo
GO
CREATE TABLE dbo.foo (
    KeyCol  char(12) NOT NULL,
    ValueCol xml NOT NULL,
    Comment varchar(1000) NULL,
    CONSTRAINT PK_foo PRIMARY KEY CLUSTERED (KeyCol)
)
GO

IF OBJECT_ID('dbo.bar') IS NOT NULL DROP PROCEDURE dbo.bar
GO
CREATE PROCEDURE dbo.bar
    @Key char(12),
    @Value xml,
    @Comment varchar(1000)
AS
SET NOCOUNT ON
DECLARE @StartTranCount tinyint;
BEGIN TRY
    SELECT @StartTranCount = @@TRANCOUNT;

    IF @StartTranCount = 0 BEGIN TRAN;

    BEGIN TRY
        --SELECT @StartTranCount = 'fish' --generates an error and goes to outer CATCH
        INSERT dbo.foo (KeyCol, ValueCol, Comment) VALUES (@Key, @Value, @Comment);
    END TRY
    BEGIN CATCH
        IF ERROR_NUMBER() = 2627    --PK violation
            UPDATE
                dbo.foo
            SET
                ValueCol = @Value, Comment = @Comment
            WHERE
                KeyCol = @Key;
        ELSE
            RAISERROR ('Tits up', 16, 1);
    END CATCH

    IF @StartTranCount = 0 COMMIT TRAN;
END TRY
BEGIN CATCH
    IF @StartTranCount = 0 AND XACT_STATE() <> 0 ROLLBACK TRAN;
    RETURN -1
END CATCH
--Without this, we'll send -4 if we hit the UPDATE CATCH block above
--RETURN 0
GO

--please run these **separately**

--Run with RETURN 0 and fish line commented out
DECLARE @rtn int
EXEC @rtn = dbo.bar 'abcdefghijkl', '<foobar />', 'testing'
SELECT @rtn; SELECT * FROM dbo.foo
GO

DECLARE @rtn int
EXEC @rtn = dbo.bar 'abcdefghijkl', '<foobar2 />', 'testing2'
--updated OK but we get @rtn = -4
SELECT @rtn; SELECT * FROM dbo.foo
GO

--uncomment fish line
DECLARE @rtn int
EXEC @rtn = dbo.bar 'abcdefghijkl', '<foobar />', 'testing'
--Hit outer CATCH, @rtn = -1 as expected
SELECT @rtn; SELECT * FROM dbo.foo

回答1:

In playing around with the procedure, I can get a a return -6, if I insert a null into foo.KeyCol and remove the RAISERROR in the inner catch. This is something SQL Server is doing, and is documented here: Return Values from Stored Procedures.