Condition check, single/multiple value for multiple columns with comma separated column

I have the following data:

create table mtest
(
 id1 int,
 id2 int,
 id3 int,
 id4 int,
 name varchar(20)
);


insert into mtest values(1,11,2,33,'Test1');
insert into mtest values(2,12,4,3,'Test2');
insert into mtest values(4,13,6,44,'Test3');
insert into mtest values(7,15,17,4,'Test4');
insert into mtest values(10,65,9,5,'Test5');
insert into mtest values(7,65,4,5,'Test6');
insert into mtest values(37,11,4,15,'Test7');

I want to find ID with the values : 7 and 4

Expected Output:

id_column   value   names
-------------------------------------
id3         4       Test2,Test6,Test7
id1         7       Test4,Test6
id1         4       Test3
id4         4       Test4

Try:

select distinct id_column,value,stuff((select ','+ name from mtest b where b.id1 = a.value or b.id2 = a.value or b.id3 = a.value or b.id4 =a.value for xml path('')), 1, 1,'') names
from
(
    select case when id1 in ('7','4') then 'id1'
                when id2 in ('7','4') then 'id2'
                when id3 in ('7','4') then 'id3'
                when id4 in ('7','4') then 'id4' else ''
            end as id_column,
            case when id1 in ('7','4') then id1
                when id2 in ('7','4') then id2
                when id3 in ('7','4') then id3
                when id4 in ('7','4') then id4 else ''
            end as value,
            name
    from mtest
) a
where a.id_column <> ''

But getting wrong result:

id_column   value   names
---------------------------------------------------
id1         4       Test2,Test3,Test4,Test6,Test7
id1         7       Test4,Test6
id3         4       Test2,Test3,Test4,Test6,Test7   

And also I am worried about stuff clause for multiple or conditions because table is having more than 10 millions of records.

Answer

You could do a UNPIVOT AND XML Path, the following query should do what you want:

;WITH CTE AS (
    SELECT Col, Val, Name
    FROM mtest a
    UNPIVOT (Val FOR Col IN ([id1],[id2],[id3],[id4])) unpiv
    WHERE Val IN (4,7) )

SELECT Col, Val, 
Name = STUFF(
             (SELECT ',' + Name 
              FROM CTE t1
              WHERE t1.Col = t2.Col AND t1.Val = t2.Val 
              FOR XML PATH (''))
             , 1, 1, '')
FROM CTE t2
GROUP BY Col, Val