SQL Column Concatenation - sql

Question

I want to concatenate the column names in my query result if the column is true. Below is the format of my data, and the format of the intended output as well as a snippet of the SQL I attempted.
DATA
ID | ColA | ColB | ColC | ColD
1 | T | F | T | F
2 | F | T | F | T
3 | T | F | T | F
4 | F | T | F | T
5 | T | F | T | F
INTENDED OUTPUT
ID | TYPE
1 | ColA,ColC
2 | ColB,ColD
3 | ColA,ColC
4 | ColB,ColD
5 | ColA,ColC
ATTEMPTED SQL
SELECT UniqueIDColumn,
CASE WHEN ColA = 1 THEN 'A' END + ', ' +
CASE WHEN ColB = 1 THEN 'B' END + ', ' +
CASE WHEN ColC = 1 THEN 'C' END + ', ' +
CASE WHEN ColD = 1 THEN 'D' END
FROM TableName

Answer 1

Easily achievable using Unpivot operator:
;WITH unpivoted AS
(
SELECT Id, Val, Col
FROM (SELECT ID, ColA, ColB, ColC, ColD FROM #Data) AS Up
UNPIVOT (Val FOR Col IN (ColA, ColB, ColC, ColD)) AS Upv
)
SELECT Id, STUFF((SELECT ', ' + Col FROM unpivoted WHERE Id = up.Id AND Val = 'T' FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 2, '') AS [Type]
FROM unpivoted up
GROUP BY Id

Answer 2

You have to write a function that receives two parameter, and, if the first parameter is true, returns the second parameter plus a delimiter (e.g., space), otherwise just the delimiter:
DROP FUNCTION IF EXISTS returnNameIfTrue;
DELIMITER $$
CREATE FUNCTION returnNameIfTrue(columnValue int, columnName varchar(10))
RETURNS varchar(10)
BEGIN
declare s varchar(10);
IF columnValue = 1 THEN
set s = concat(columnName , ' ');
else
set s = ' ';
END IF;
RETURN s;
END;
$$
DELIMITER ;
Then, the solution will be:
select id, rtrim(concat(returnNameIfTrue(colA, 'colA'),
returnNameIfTrue(colB, 'colB'),
returnNameIfTrue(colC, 'colC'),
returnNameIfTrue(colD, 'colD'))) as type
from tableName
Or, if you also want to get rid of additional space:
select id, replace(replace(replace(rtrim(concat(returnNameIfTrue(colA, 'colA'),
returnNameIfTrue(colB, 'colB'),
returnNameIfTrue(colC, 'colC'),
returnNameIfTrue(colD, 'colD'))), ' ', ' '), ' ', ' '), ' ', ' ') as type
from tableName