Question

Newbie question. I want to do something like:

SELECT c1,c2,c3 FROM TABLE t1
UNION
SELECT c1,c2,c3 FROM TABLE t2 WHERE t1.c1 IS NOT NULL AND t1.c2 IS NULL;

so if I have t1:

c1|c2|c3
1 | a|v1
2 | b|v2

and t2:

c1|c2|c3
1 | a|v3
2 | b|v4
2 | c|v5
3 | d|v6

I would get:

c1|c2|c3
1 | a|v1
2 | b|v2
2 | c|v5

Anybody knows how to do this?

Answer 1

According to SQL Docs, JOIN is faster that SubQueries. try this:

 SELECT c1, c2, c3
 FROM   t1
 UNION
 SELECT b.c1, b.c2, b.c3
 FROM   t1 a inner join t2 b ON
         (a.c1 = b.c1) and (a.c1 = b.c1)
 WHERE  (b.c1,b.c2) NOT IN (SELECT c1,c2 FROM t1)

to prove, see here: http://sqlfiddle.com/#!2/50a4e/23