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Overview
| Comment: | Clarification of text in the new optoverview.html section on the LEFT JOIN Optimization. |
|---|---|
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
9e6750c1fc9dc1a8c44ebaf375b6f7f5 |
| User & Date: | drh 2018-03-23 14:53:01 |
Context
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2018-03-23
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| 17:42 | Updates to the whyc.html and assert.html documentation pages. check-in: e7ab215c5b user: drh tags: trunk | |
| 14:53 | Clarification of text in the new optoverview.html section on the LEFT JOIN Optimization. check-in: 9e6750c1fc user: drh tags: trunk | |
| 14:46 | Update syntax diagrams and expression text to cover the new TRUE and FALSE literals and the IS TRUE and IS FALSE operators. check-in: dfdf980e6c user: drh tags: trunk | |
Changes
Changes to pages/optoverview.in.
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changing the result. This can happen if all of the following are
true:
<p>
<ol>
<li> The query is not an aggregate
<li> Either the query is DISTINCT or else the ON or USING clause
on the LEFT JOIN must constrains the join such that it matches
only a single row
<li> The right-hand table of the LEFT JOIN must not be used anywhere
in the query outside of its own USING or ON clause.
</ol>
<p>
LEFT JOIN elimination often comes up when LEFT JOINs are used
inside of views, and then the view is used in such as way that
none of the columns of the right-hand table of the LEFT JOIN are
|
| | |
1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 |
changing the result. This can happen if all of the following are
true:
<p>
<ol>
<li> The query is not an aggregate
<li> Either the query is DISTINCT or else the ON or USING clause
on the LEFT JOIN constrains the join such that it matches
only a single row
<li> The right-hand table of the LEFT JOIN is not be used anywhere
in the query outside of its own USING or ON clause.
</ol>
<p>
LEFT JOIN elimination often comes up when LEFT JOINs are used
inside of views, and then the view is used in such as way that
none of the columns of the right-hand table of the LEFT JOIN are
|