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copied!<p>IMHO you either join your tables if they're related to each other. One way to do it if <code>col1</code> is the common column </p> <pre><code>SELECT COALESCE(m.col1, d.col1, e.col1) column_name1, m.col2 column_name2, m.col3 column_name3, d.col2 column_name4, e.col2 column_name5 FROM messages m FULL JOIN messagedata d ON m.col1 = d.col1 FULL JOIN extradata e ON d.col1 = e.col1 </code></pre> <p>Sample output:</p> <pre> | COLUMN_NAME1 | COLUMN_NAME2 | COLUMN_NAME3 | COLUMN_NAME4 | COLUMN_NAME5 | |--------------|--------------|--------------|--------------|--------------| | 1 | value12 | value13 | data1 | extradata1 | | 2 | value21 | value31 | data2 | extradata2 | </pre> <p>or you <code>UNION</code> them in this way</p> <pre><code>SELECT col1 column_name1, col2 column_name2, col3 column_name3 FROM messages UNION ALL SELECT col1, col2, NULL FROM messagedata UNION ALL SELECT col1, NULL, NULL FROM extradata </code></pre> <p><strong>Note</strong> that the number of columns and their respective data types should be the same for all <code>SELECT</code>s that you <code>UNION</code>. To overcome this you can inject constant values (e.g. <code>NULL</code>) and convert/cast column values to some common type (e.g. <code>VARCHAR2</code>) if needed.</p> <p>Sample output:</p> <pre> | COLUMN_NAME1 | COLUMN_NAME2 | COLUMN_NAME3 | |--------------|--------------|--------------| | 1 | value12 | value13 | | 2 | value21 | value31 | | 1 | data1 | (null) | | 2 | data2 | (null) | | 1 | (null) | (null) | | 2 | (null) | (null) | </pre> <p>Here is <strong><a href="http://sqlfiddle.com/#!4/83cea/3" rel="nofollow">SQLFiddle</a></strong> demo</p>

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