[MYSQL] select multiple columns without comma

# using comma
mysql> select id,pw from users 
+-------+-------+
| id    | pw    |
+-------+-------+
| admin | admin |
| guest | guest |
+-------+-------+
2 rows in set (0.01 sec)

# without comma
mysql> select * fom (select id from user)a join (select pw from user)b;	
+-------+-------+
| id    | pw    |
+-------+-------+
| admin | admin |
| guest | admin |
| admin | guest |
| guest | guest |
+-------+-------+
4 rows in set (0.01 sec)

# union select without comma
mysql> select id,pw from user union select * from (select 1)a join (select 2)b;
+-------+-------+
| id    | pw    |
+-------+-------+
| admin | admin |
| guest | guest |
| 1     | 2     |
+-------+-------+
3 rows in set (0.00 sec)