Question

I would like to find a quick method for debugging a insert-select statement.
Example:

Create table tbl_int (
        tabid int identity,
        col1 bigint)

Create table tbl_char(
        tabid int identity,
        col2 nvarchar(255))


insert into tbl_char(col2) 
    select '1' union 
    select '2' union
    select 'a'

insert into tbl_int(col1)
    select col2 
    from tbl_char

Of course, the insert select above fails to run and it is obvious that ‘a’ cannot be converted to bigint. But what happens when I have 1 milion records in tbl_char. Is there any way of finding the source value of the error:
“Error converting data type nvarchar to bigint.”
P.s. Using a convert or cast function and scanning the table with top until finding the right value is a little bit too expensive.

Answer 1

Why don’t you wrap the SQL that throw the exception into a Try/Catch block to have more info about it

BEGIN TRY
    SELECT *
        FROM sys.messages
        WHERE message_id = 21;
END TRY
GO
-- The previous GO breaks the script into two batches,
-- generating syntax errors. The script runs if this GO
-- is removed.
BEGIN CATCH
    SELECT ERROR_NUMBER() AS ErrorNumber;
END CATCH;
GO

the below are all the error information you can check

ERROR_NUMBER() returns the error number.

ERROR_MESSAGE() returns the complete text of the error message. The text includes the values supplied for any substitutable parameters such as lengths, object names, or times.

ERROR_SEVERITY() returns the error severity.

ERROR_STATE() returns the error state number.

ERROR_LINE() returns the line number inside the routine that caused the error.

ERROR_PROCEDURE() returns the name of the stored procedure or trigger where the error occurred.

http://msdn.microsoft.com/en-us/library/ms179296.aspx

if this is not enough you can even write a query to select all the records where certain field is not convertible to a number(in your case there is a NVarChar which is not convertible)

The following example uses ISNUMERIC to return all the postal codes that are not numeric values.

SELECT City, PostalCode
FROM Person.Address 
WHERE ISNUMERIC(PostalCode)<> 1

http://msdn.microsoft.com/en-us/library/ms186272.aspx