a wierd query

hi

i have a wierd problem and i require an equally weird query.
1) backgound
Table test:
CREATE TABLE main_table (
string_A varchar( 20),
string_B varchar( 20),
);
-- both columns are identical in nature and usage
INSERT INTO main_table VALUES('abcd','qrst');
INSERT INTO main_table VALUES('efgh','efgh');
INSERT INTO main_table VALUES('ijkl','abcd');
INSERT INTO main_table VALUES('abcd','ijkl');
INSERT INTO main_table VALUES('qrst','uvwx');

2) problem:

i require a query that gives me a result set of the form

'abcd'
'efgh'
'ijkl'
'qrst'
'uvwx'

that is i require the dictinct values from (visualizing each column
result as a set) the union of the two columns

3) questions

a) is a query like this possible that can give me the desired result
b) if so what would it be.

4) remarks

i can get the solution using a temporary table and with repeated
"insert into temporary select $column from main_table"

thanks in advance

ashok

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