MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE t1 (Sortder varchar(100), id int)
INSERT INTO t1 VALUES ('1,2,3,4',0),('4,3,2,1',1)
CREATE TABLe t2 (f1 int, val varchar(10))
INSERT INTO t2 VALUES (1,'a'),(2,'b'),(3,'c'),(4,'d')
SELECT * FROM t2
ORDER BY
CASE WHEN  4 = 5
THEN  find_in_set( f1, (SELECT Sortder FROM t1 WHERE id = 0) )
ELSE find_in_set( f1, (SELECT Sortder FROM t1 WHERE id = 1) )
END


f1
val


4
d

3
c

2
b

1
a


SELECT * FROM t2
ORDER BY
CASE WHEN  5 = 5
THEN  find_in_set( f1, (SELECT Sortder FROM t1 WHERE id = 0) )
ELSE find_in_set( f1, (SELECT Sortder FROM t1 WHERE id = 1) )
END


f1
val


1
a

2
b

3
c

4
d