Question

I’ve this table

col 1   col 2   col 3   ....    col N
-------------------------------------
1       A       B               fooa        
10      A       foo             cc
4       A       B               fooa

it is possible with a tsql query to return only one row with a value only where the values are ALL the same?

col 1   col 2   col 3   ....    col N
-------------------------------------
--      A       --              --

Answer 1

SELECT
     CASE WHEN COUNT(col1) = COUNT(*) AND MIN(col1) = MAX(col1) THEN MIN(col1) END AS col1,
     CASE WHEN COUNT(col2) = COUNT(*) AND MIN(col2) = MAX(col2) THEN MIN(col2) END AS col2,
     ...
FROM yourtable

You have to allow for NULLs in the column:

• COUNT(*) counts them
• COUNT(col1) doesn’t count them

That is, a columns with a mix of As and NULLs isn’t one value. MIN and MAX would both give A because they ignore NULLs.

Edit:

• removed DISTINCT to get counts the same for NULL check
• added MIN/MAX check (as per Mark Byers deleted answer) to check uniqueness