DB2 学习笔记 - AIView.com

See following SQL

SELECT DISTINCT c1 FROM t1
UNION
SELECT c1 FROM t2
@ 

We could remove DISTINCT safely. UNION will do what DISTINCT does here. See following sample.

SELECT c1 FROM t1@

c1
----
1
1
2

SELECT c1 FROM t2@

c1
----
2
3
3 

SELECT c1 FROM t1
UNION
SELECT c1 FROM t2
@ 

c1
----
1
2
3