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POSomething strange in mysql query because of Group By Statement
 

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  1. POSomething strange in mysql query because of Group By Statement
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    <p>I have this table which recording exam results for the users:</p> <pre><code>CREATE TABLE IF NOT EXISTS `ts` ( `id` int(11) NOT NULL AUTO_INCREMENT, `uid` int(11) NOT NULL, `xid` int(11) NOT NULL, `lid` int(11) NOT NULL, `grade` double NOT NULL, `duration` varchar(10) COLLATE utf8_turkish_ci NOT NULL, `trues` int(11) NOT NULL DEFAULT '0', `falses` int(11) NOT NULL DEFAULT '0', `empties` int(11) NOT NULL DEFAULT '0', PRIMARY KEY (`id`), KEY `uid` (`uid`), KEY `xid` (`xid`), KEY `lid` (`lid`), ) ENGINE=InnoDB; </code></pre> <p>And I have this records in the table:</p> <pre><code>|id|uid|xid|lid|grade|duration|trues|falses|empties| +--+---+---+---+-----+--------+-----+------+-------+ |45| 20| 1| 1| 80|00:01:12| 8| 2| 0| |46| 20| 1| 2| 40|00:02:31| 4| 6| 0| |47| 20| 3| 1| 100|00:01:10| 1| 0| 0| |48| 20| 4| 1| 83|00:00:51| 5| 1| 0| |49| 20| 2| 1| 0|00:00:02| 0| 1| 0| |53| 20| 4| 2| 50|00:00:04| 1| 1| 0| |54| 20| 1| 2| 50|00:00:41| 5| 5| 0| </code></pre> <p><code>lid</code> indicates the difficulty level of exam which is represented by <code>xid</code>. I want to show the highest grades for each unique exams with unique levels. For example there are 7 rows. and id[46] and id[54] are for the same exams and levels. So I must list the higher grade value among these two rows.</p> <p>I have made a query:</p> <pre><code>SELECT failed.fgrade, succeeded.sgrade, ts.xid, ts.lid, ts.trues, ts.falses, ts.empties, MAX(`grade`) AS grade, ts.duration, x.exam FROM ts JOIN x ON ts.xid = x.id JOIN (SELECT COUNT(DISTINCT(xid)) AS sgrade FROM ts WHERE uid = 20 AND grade &gt;= 70) AS succeeded JOIN (SELECT COUNT(DISTINCT(xid)) AS fgrade FROM ts WHERE uid = 20 AND grade &lt; 70 ) AS failed WHERE ts.uid = 20 GROUP BY xid, lid ORDER BY ts.id </code></pre> <p>When I run the query I get strange result:</p> <pre><code>Exam Name Level Duration True False Empty Total Grade fgrade sgrade Functions 1 00:00:02 0 1 0 1 0 3 3 Numbers 2 00:02:31 4 6 0 10 50 3 3 (!) Equations 2 00:00:04 1 1 0 2 50 3 3 Numbers 1 00:01:12 8 2 0 10 80 3 3 Equations 1 00:00:51 5 1 0 6 83 3 3 Functions 1 00:01:10 1 0 0 1 100 3 3 </code></pre> <p>If you look at the (!) row in the result table there is something weird. 4 correct answers and 6 false answers make 40 points. But it shows the other row's grade value while showing own true and false answer counts.</p> <p>I am basically wishing to show the all different exams for each difficulty levels for a given userid (<code>uid</code>). Now as I am writing this question, I am starting to think that it may be due to the <code>GROUP BY</code> statement. But it has taken a while to write the question. I cannot delete this.</p>
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    1. USzkanoca
    1. USzkanoca
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    1. COWhere's the `ON` for your last 2 joins? Really, why are those joins even there?
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      1. POSomething strange in mysql query because of Group By Statement
      1. USHart CO
 

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