T-SQL Case Statement in a JOIN ON Clause

Question

I am trying to build a case/if statement in a JOIN ON clause.

LEFT JOIN [CTSTRC] [Statuses] ON RIGHT([Statuses].[STRID], 3) = [CTE].[F61]

The problem is that the column [Statuses].[STRID] contains text and numbers. The column I am comparing it to [CTE].[F61] is an integer.

Is there a way to detect if column [Statuses].[STRID] has a character or a number and THEN set it to 0 if it is a character?

Here is a pseudo query to help:

LEFT JOIN [CTSTRC] [Statuses] 
    ON RIGHT((
        CASE [Statuses].[STRID] 
            WHEN TEXT THEN 0 
            ELSE CAST([Statuses].[STRID] AS INT) END), 3) = [CTE].[F61]

Answer 1

You're looking for IsNumeric but it doesn't always work (+,- and . are numeric) so you need to use the solution described by GBN which is to add .0e0 to your varchar

LEFT JOIN [CTSTRC] [Statuses] ON 
    (CASE WHEN ISNUMERIC(RIGHT([Statuses].[STRID], 3) + '.0e0) = 1 
          THEN  CAST(RIGHT([Statuses].[STRID], 3) AS INT) 
          ELSE 0  END) = [CTE].[F61] 

Answer 2

create a persisted computed column and add an index on it.

ALTER TABLE YourTable ADD
    NewIntID AS (CASE ISNUMERIC(RIGHT([Statuses].[STRID], 3) + '.0e0)
                     WHEN 1 THEN CAST(RIGHT([Statuses].[STRID], 3) AS INT) 
                     ELSE 0
                 END) PERSISTED
GO

CREATE INDEX IX_YourTable_NewIntID 
ON YourTable (NewIntID ); 
GO

you can now just join to the new NewIntID column as if it were the proper numeric ID now.