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
$columnfrom main_table" 


thanks in advance

ashok

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