How do I get distinct count values of 2 columns?

Question

Lets say I have 2 columns, a and b.

Column A contains these values:

a
b
c
d

Column B contains these values:

e
d
c
b
a

What can I do to get the absolute distinct values from BOTH columns?

Meaning if i want to have a count on both columns, the result is to be 5. Because a, b, c and d are repeated in column B but not e.

Answer 1

SELECT A
FROM YourTable
UNION
SELECT B
FROM YourTable