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    <p>You should to union both columns and then filter for distinct values:</p> <pre><code>select distinct T.from_to from ( select `from` as from_to from messages union select `to` as from_to from messages ) T </code></pre> <p>if you really need all in a comma separate string, use <a href="http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat" rel="nofollow">GROUP_CONCAT([DISTINCT]</a> aggregation function.</p> <p><strong>EDITED</strong>:</p> <p>You should mark as solution Gerald answer. After test union operator and reread <a href="http://dev.mysql.com/doc/refman/5.0/en/union.html" rel="nofollow">mysql union operator documentation</a>, by default, mysql filter for distinct values:</p> <pre><code>mysql&gt; create table ta( a int ); Query OK, 0 rows affected (0.05 sec) mysql&gt; insert into ta values (1),(1),(2); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql&gt; select * from ta -&gt; union -&gt; select * from ta; +------+ | a | +------+ | 1 | | 2 | +------+ 2 rows in set (0.00 sec) </code></pre> <p>then, the <strong>final query</strong> is:</p> <pre><code> select `from` as from_to from messages union distinct select `to` as from_to from messages </code></pre> <p>Notice that <code>distinct</code> is not mandatory.</p> <p>Only if you need a comma sparate string the first solution is necessary:</p> <pre><code>select distinct GROUP_CONCAT( distinct T.from_to from ) ( select `from` as from_to from messages union select `to` as from_to from messages ) T </code></pre>
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    1. POsql distinct, getting 2 columns
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    1. USdani herrera
    1. USdani herrera
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    1. COthank you danihp, you just saved my day :|
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      1. USRoth zerg
    2. COYou do not need the outer distinct, as UNION selects distinct rows by default. UNION ALL allows for duplicates.
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      1. USGerald P. Wright
    3. CO@GeraldP.Wright, yes read updated answer.
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