Pull Columns based on row value - sql

Question

I have a table X
ID A B C D
1 T T F T
2 F T F T
3 T F T F
So if my input is 1 for ID, then I want all column names that have value T for row 1. In above case A,B,D or If ID is 3 then A and C.
How could I list these columns?

Answer 1

You can use UNPIVOT for this
SELECT Y
FROM Table1
UNPIVOT (X FOR Y IN ([A], [B], [C], [D])) U
WHERE [ID] = 1 AND X = 'T'
Returns
+---+
| Y |
+---+
| A |
| B |
| D |
+---+
SQL Fiddle

Answer 2

Also you can use XQuery with powerful FLWOR Expression. And no matter how many columns contains a table;)
SELECT(
SELECT *
FROM Table1 t
WHERE ID = 1
FOR XML PATH(''), TYPE
).query(
'for $spec in ./*
where $spec [contains(., "T")]
return fn:local-name($spec)'
) o
Demo on SQLFiddle
This decision returns the names of columns on each row
SELECT o.TCols.value('.', 'nvarchar(100)') AS T
FROM(SELECT(
            SELECT *     
            FROM Table1 t
            WHERE ID = 1
            FOR XML PATH(''), TYPE
            ).query('
                     for $spec in ./*
                     where $spec [contains(., "T")]           
                     return (
                             <TCols>
                               {fn:local-name($spec)}
                             </TCols>
                             )
                     ')) t(TCols) CROSS APPLY T.TCols.nodes('/TCols') o(TCols)
Results
+---+
| T |
+---+
| A |
| B |
| D |
+---+
Demo on SQLFiddle

Answer 3

In case that you know the number and name of all columns, you may do the below
SELECT case A when 'T' then 'A' else '' end
+ case B when 'T' then ',B' else '' end
+ case C when 'T' then ',C' else '' end
+ case D when 'T' then ',D' else '' end
FROM
Table1
WHERE ID = 1