This question could easily take multiple paths, so I will hit the more specific path first. While working with SQL Server 2005, I’m trying to create a scalar function that acts as a ‘TryCast’ from varchar to int. Where I encounter a problem is when I add a TRY block in the function;
CREATE FUNCTION u_TryCastInt
(
@Value as VARCHAR(MAX)
)
RETURNS Int
AS
BEGIN
DECLARE @Output AS Int
BEGIN TRY
SET @Output = CONVERT(Int, @Value)
END TRY
BEGIN CATCH
SET @Output = 0
END CATCH
RETURN @Output
END
Turns out theres all sorts of things wrong with this statement including “Invalid use of side-effecting or time-dependent operator in ‘BEGIN TRY’ within a function” and “Invalid use of side-effecting or time-dependent operator in ‘END TRY’ within a function”. I can’t seem to find any examples of using try statements within a scalar function, which got me thinking, is error handling in a function is possible?
The goal here is to make a robust version of the Convert or Cast functions to allow a SELECT statement carry through depsite conversion errors. For example, take the following;
CREATE TABLE tblTest
(
f1 VARCHAR(50)
)
GO
INSERT INTO tblTest(f1) VALUES('1')
INSERT INTO tblTest(f1) VALUES('2')
INSERT INTO tblTest(f1) VALUES('3')
INSERT INTO tblTest(f1) VALUES('f')
INSERT INTO tblTest(f1) VALUES('5')
INSERT INTO tblTest(f1) VALUES('1.1')
SELECT CONVERT(int,f1) AS f1_num FROM tblTest
DROP TABLE tblTest
It never reaches point of dropping the table because the execution gets hung on trying to convert ‘f’ to an integer. I want to be able to do something like this;
SELECT u_TryCastInt(f1) AS f1_num FROM tblTest
fi_num
__________
1
2
3
0
5
0
Any thoughts on this? Is there anything that exists that handles this? Also, I would like to try and expand the conversation to support SQL Server 2000 since Try blocks are not an option in that scenario.
Check if you can convert to int first, check out the IsInteger function here: IsNumeric, IsInt, IsNumber It will work on 2000 and up