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a wierd query

From: "ashok(at)kalculate(dot)com" <ashok(at)kalculate(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: a wierd query
Date: 2004-05-13 08:07:08
Message-ID: (view raw or whole thread)
Lists: pgsql-sql

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


   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


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