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    <p>This query:</p> <pre><code> SELECT * FROM notifications n WHERE 1 GROUP BY `from` </code></pre> <p>is simply wrong in ANSI SQL and on almost all DBMS (oracle, postgres, MS SQL etc.).<br> <br> It runs on MySql only because of their nonstandard <code>group by extension</code><br> See this link: <a href="http://dev.mysql.com/doc/refman/5.0/en/group-by-extensions.html" rel="nofollow">http://dev.mysql.com/doc/refman/5.0/en/group-by-extensions.html</a> <br><br> Hovever they warn about something:</p> <blockquote> <p>However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are <strong>indeterminate</strong>.</p> </blockquote> <p>Because of this "feature" your query (select from select * group by) is unpredicable, results are dependent on the order of records in the table.<br> Take a look at this simple demo: <a href="http://www.sqlfiddle.com/#!2/b762e/2" rel="nofollow">http://www.sqlfiddle.com/#!2/b762e/2</a> <br>There are two identic tables in this demo, with the same content, the only difference is a physical rows order. And the same queries give completely different results.</p> <p><br><br> <strong>---- EDIT how to solve this problem -----</strong></p> <p>To solve this problem in your query, just add both columns to the GROUP BY clause.</p> <pre><code>select * FROM ( SELECT * FROM notifications n GROUP BY `from`, `group_id` ) x WHERE group_id = 'A'; select * FROM ( SELECT * FROM notifications n WHERE group_id = 'A' GROUP BY `from`, `group_id` ) x </code></pre> <p>Above two queries give always the same results for columns <code>from</code> and <code>group_id</code>, other columns (not included in the GROUP BY clause`) can be random.<br> Take a look at simple demo --> <a href="http://www.sqlfiddle.com/#!2/5d19b/5" rel="nofollow">http://www.sqlfiddle.com/#!2/5d19b/5</a></p>
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    1. POWhy is this group by query not working?
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    1. USkrokodilko
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    1. POWhy is this group by query not working?
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    1. CO+1 for the fiddle! I'm using mysql so I don't mind that this is not standard sql. I updated the question to clarify that the issue wasn't which result was getting returned, I'm familiar with that problem. But that one row was being excluded complete when doing the outer group by. I also confirmed this by adding a count(id) to add up the results. If I put the group by on the inside, the numbers add up to 7 and I have all 4 entries, if I put the group by on the the outside, the counts add up to 6.
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    2. CO@Yehosef I edited my answer and appended a solution to this problem.
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    3. COnevermind - I see the problem now. thanks!
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