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Oliver Kennedy 2018-01-31 13:40:33 -05:00
parent 5ef5579d77
commit b66d675d4e
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slides/cse4562sp2018/2018-01-31-SQL+Physical.html
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@ -237,7 +237,7 @@
SELECT tree_id FROM Trees WHERE spc_common = 'sycamore maple'
</code></pre>
<p style="font-size: 70%">Computes the <b>set-union</b> of any two <b>union-compatible</b> sets of tuples</p>
<p style="font-size: 70%">Adding <code>ALL</code> preserves duplicates across the inputs.</p>
<p style="font-size: 70%">Adding <code>ALL</code> preserves duplicates across the inputs (<b>bag-union</b>).</p>
</section>
<section>
@ -247,15 +247,13 @@
FROM relationlist
WHERE condition
GROUP BY groupinglist
HAVING group-condition
HAVING groupcondition
</code></pre>
<div style="font-size: 70%">
<p>The target-list now contains...<ol class="tight" style="margin-top: 0px; margin-left: 100px;">
<li>grouped attributes</li>
<li>aggregate expressions</li>
</ol></p>
<p>Targets of type (1) must be a subset of the grouping-list</p>
<p>The <span color="red">targetlist</span> now contains <b>(a)</b> Grouped attributes, and <b>(b)</b>Aggregate expressions.</p>
<p>Targets of type (a) must be a subset of the grouping-list</p>
<p style="font-size: 70%">(intuitively each answer tuple corresponds to a single group, and each group must have a single value for each attribute)</p>
<p style="margin-top: 20px"><span color="red">groupcondition</span> is applied <i>after</i> aggregation and may contain aggregate expressions.</p>
</div>
</section>