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Overview
| Comment: | Fix another typo in the query planner document. |
|---|---|
| Timelines: | family | ancestors | descendants | both | branch-3.10 |
| Files: | files | file ages | folders |
| SHA1: |
47810e77efe44839b8e390ee9a8ce91f |
| User & Date: | drh 2016-01-14 17:58:19 |
Context
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2016-01-19
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| 17:07 | Add documentation for sqlite3_analyzer.exe and support for the "tools" download bundles. check-in: dd586d2857 user: drh tags: branch-3.10 | |
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2016-01-14
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| 18:26 | Merge updates from the 3.10 branch. check-in: 885e891911 user: drh tags: trunk | |
| 17:58 | Fix another typo in the query planner document. check-in: 47810e77ef user: drh tags: branch-3.10 | |
| 16:10 | Fix typos in queryplaner.html check-in: 316be08907 user: drh tags: branch-3.10 | |
Changes
Changes to pages/queryplanner.in.
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<tcl>figure 18 #fig18 obfruitidx1.gif {Sorting With An Index}</tcl>
<p>
The Idx1 index is scanned from top to bottom (or from bottom to top if
"ORDER BY fruit DESC" is used) in order to find the rowids for each item
in order by fruit. Then for each rowid, a binary search is done to lookup
and output that row. In this way, the output appears in the requested order
with the need to gather then entire output and sort it using a separate step.
</p>
<p>
But does this really save time? The number of steps in the
<a href="#fig16">original indexless sort</a> is proportional to NlogN since
that is how much time it takes to sort N rows. But when we use Idx1 as
shown here, we have to do N rowid lookups which take logN time each, so
|
| |
549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 |
<tcl>figure 18 #fig18 obfruitidx1.gif {Sorting With An Index}</tcl>
<p>
The Idx1 index is scanned from top to bottom (or from bottom to top if
"ORDER BY fruit DESC" is used) in order to find the rowids for each item
in order by fruit. Then for each rowid, a binary search is done to lookup
and output that row. In this way, the output appears in the requested order
without the need to gather the entire output and sort it using a separate step.
</p>
<p>
But does this really save time? The number of steps in the
<a href="#fig16">original indexless sort</a> is proportional to NlogN since
that is how much time it takes to sort N rows. But when we use Idx1 as
shown here, we have to do N rowid lookups which take logN time each, so
|