EMP EMP - 5 months ago 87
SQL Question

How to report an error from a SQL Server user-defined function

I'm writing a user-defined function in SQL Server 2008. I know that functions cannot raise errors in the usual way - if you try to include the RAISERROR statement SQL returns:

Msg 443, Level 16, State 14, Procedure ..., Line ...
Invalid use of a side-effecting operator 'RAISERROR' within a function.


But the fact is, the function takes some input, which may be invalid and, if it is, there is no meaningful value the function can return. What do I do then?

I could, of course, return NULL, but it would be difficult for any developer using the function to troubleshoot this. I could also cause a division by zero or something like that - this would generate an error message, but a misleading one. Is there any way I can have my own error message reported somehow?

Answer

You can use CAST to throw meaningful error:

create function dbo.throwError()
returns nvarchar(max)
as
begin
    return cast('Error happened here.' as int);
end

Then Sql Server will show some help information:

Msg 245, Level 16, State 1, Line 1
Conversion failed when converting the varchar value 'Error happened here.' to data type int.
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