Error converting data type varchar

Question

I currently have a table with a column as varchar. This column can hold numbers or text. During certain queries I treat it as a bigint column (I do

Answer 1

Ideally, you want to try to avoid storing the data in this form - would be worth splitting the BIGINT data out in to a separate column for both performance and ease of querying.

However, you can do a JOIN like this example. Note, I'm not using ISNUMERIC() to determine if it's a valid BIGINT because that would validate incorrect values which would cause a conversion error (e.g. decimal numbers).

DECLARE @MyTable TABLE (MyCol VARCHAR(20))
DECLARE @OtherTable TABLE (Id BIGINT)

INSERT @MyTable VALUES ('1')
INSERT @MyTable VALUES ('Text')
INSERT @MyTable VALUES ('1 and some text')
INSERT @MyTable VALUES ('1.34')
INSERT @MyTable VALUES ('2')
INSERT @OtherTable VALUES (1)
INSERT @OtherTable VALUES (2)
INSERT @OtherTable VALUES (3)

SELECT *
FROM @MyTable m
    JOIN @OtherTable o ON CAST(m.MyCol AS BIGINT) = o.Id
WHERE m.MyCol NOT LIKE '%[^0-9]%'

Update: The only way I can find to get it to work for having a WHERE clause for a specific integer value without doing another CAST() on the supposedly bigint column in the where clause too, is to use a user defined function:

CREATE  FUNCTION [dbo].[fnBigIntRecordsOnly]()
RETURNS @Results TABLE (BigIntCol BIGINT)
AS
BEGIN
INSERT @Results
SELECT CAST(MyCol AS BIGINT)
FROM MyTable
WHERE MyCol NOT LIKE '%[^0-9]%'
RETURN
END

SELECT * FROM [dbo].[fnBigIntRecordsOnly]() WHERE BigIntCol = 1

I don't really think this is a great idea performance wise, but it's a solution