Error handling in T-SQL scalar function

Question

This question can easily take several paths, so I will first hit a more specific path. While working with SQL Server 2005, I am trying to create a scalar function that acts like "TryCast" from varchar to int. Where I ran into a problem when I add a TRY block to a 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

It turns out that with this statement everything is wrong, including "Invalid use of side effect or time-dependent statement in" BEGIN TRY "inside a function" and "Invalid use of side effect or time-dependent statement in" END TRY "inside a function." I can't seem to find examples of using try statements in a scalar function that made me think if error handling in the function is possible?

, Convert Cast, SELECT depsite. , :

    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

, 'f' . - :

SELECT u_TryCastInt(f1) AS f1_num FROM tblTest

fi_num
__________
1
2
3
0
5
0

? -, ? , SQL Server 2000, Try.

Answer 1

, int, IsInteger: IsNumeric, IsInt, IsNumber 2000

Answer 2

, : , try-catch . , - , , , , .

, , , ... - . , , NULL.

Answer 3

TRY... CATCH SQL 2012!

: http://msdn.microsoft.com/en-us/library/ms175976.aspx

script:

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

:

Msg 443, 16, 14, u_TryCastInt, 10
"BEGIN TRY" .
Msg 443, 16, 14, u_TryCastInt, 12
"END TRY" .
Msg 443, 16, 14, u_TryCastInt, 13
"BEGIN CATCH" .
Msg 443, 16, 14, u_TryCastInt, 15
"END CATCH" .