How to MAX() on any column type at SQL Server

Question

I have a view with many columns and a query builder that will eventually add a MAX statement on the query. Problem is, when the column type is BIT I cannot use MAX on it, so I need to check type before. I cannot check the data type of the column during the query builder, so I need a SQL solution that works fine for any data type.

Here is an example (the SELECT within the CTE represents a VIEW which can have any type of data on mycol , for this first example I'm simulating a BIT . The MAX portion is where I need to work on):

ORIGINAL

WITH cte (mycol) AS 
(
    SELECT CAST(1 as BIT) as mycol
)
SELECT
    MAX(mycol) as mycol_max
FROM cte

I got this error:

Operand data type bit is invalid for max operator.

CASTING

If I do the following it will work:

WITH cte (mycol) AS
(
     SELECT CAST(1 as BIT) as mycol
)
SELECT
    MAX(CAST(mycol as INT)) as mycol_max
FROM cte

However, if mycol is a string (SELECT 'test' as mycol), I got this error:

Conversion failed when converting the varchar value 'test' to data type int.

So, I tried to check type using some different approaches:

ISNUMERIC()

WITH cte (mycol) AS
(
     SELECT 'test' as mycol
)
SELECT
    MAX(CASE 
           WHEN 1 = ISNUMERIC(mycol) 
              THEN CAST(mycol AS INT) 
              ELSE mycol 
        END) AS mycol_max
FROM cte

NOT LIKE %[^0-9]%

WITH cte (mycol) AS
(
     SELECT 'test' as mycol
)
SELECT
    MAX(CASE 
           WHEN "mycol" NOT LIKE '%[^0-9]%' 
              THEN CAST(mycol AS INT) 
              ELSE mycol 
        END) AS mycol_max
FROM cte;

TRY_PARSE

WITH cte (mycol) AS 
(
     SELECT 'test' as mycol
)
SELECT
    MAX(CASE 
           WHEN TRY_PARSE(mycol AS INT) IS NOT NULL 
              THEN CAST(mycol AS INT) 
           ELSE mycol 
        END) AS mycol_max
FROM cte

All of these returned the error

Conversion failed when converting the varchar value 'test' to data type int.

Also, if mycol is an integer:

WITH cte (mycol) AS
(
     SELECT 1 as mycol
)
...

I got

Argument data type int is invalid for argument 1 of parse function.

So, all I need is to allow anything into the MAX() statement. I tried checking and converting, but didn't get any satisfactory solution. How can I do it?

Thanks

Using SQL Server 2017.

Answer 1

BIT Won't behave as int so MAX won't really work unless you just choose max LEN which is still not optimal. You might try ORDER BY DESC but I doubt it will help. You might as well add another column that will specify what exactly MAX you're looking for.

SELECT TOP 1 CAST(1 as BIT) as mycol
FROM TB1
ORDER BY mycol DESC