Question

I need help to formulate a query. I want to select all DISTINCT colors from TABLE A and TABLE B.

This is the wanted result from the query:

BLACK
RED
YELLOW
BLUE

I have these tables:

TABLE A

ID   NAME    COLOR
5    SOCKS   BLACK
4    SOCKS   RED

TABLE B

ID   NAME   COLOR 
0    CAR    BLUE
1    BIKE   BLUE
5    TRUCK  YELLOW
10   PLANE  NULL

I have tried:

SELECT DISTINCT A.color FROM A JOIN B ON b.color

But I don’t get all the colors. 🙁

Answer 1

SELECT color FROM A
UNION
SELECT color FROM B
WHERE  color IS NOT NULL -- only filters NULL from B
ORDER  BY color          -- sorts all rows

UNION (instead of UNION ALL) removes duplicates. No need for additional subqueries or DISTINCT.