mysql 组合两列

Question

I need a little help in mysql. I have a table(say tablea ) like this

tablea
--------------------------------------------
col1                         col2
a                            1
b                            1
c                            1
h                            3
d                            2
e                            2
f                            2
--------------------------------------------

After combining, my output should be

col3
--------
1
a
b
c
3
h
2
d
e
f
--------

Any idea on how to get this output?

Answer 1

Use the UNION operator, like so:

SELECT col1 AS col3
FROM tablea

UNION ALL

SELECT col2 AS col3
FROM tablea