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'v3.4.2.55'
2016-04-17 15:48:03 +00:00
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<h1 id="firstHeading" class="firstHeading"><span>Dev/Sqlite/Tips</span></h1>
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<div id="siteSub">From XOWA: the free, open-source, offline wiki application</div>
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<h2>
Contents
</h2>
</div>
<ul>
<li class="toclevel-1 tocsection-1">
<a href="#Avoid_LIKE"><span class="tocnumber">1</span> <span class="toctext">Avoid LIKE</span></a>
</li>
<li class="toclevel-1 tocsection-2">
<a href="#Alternative:_Use_comparison"><span class="tocnumber">2</span> <span class="toctext">Alternative: Use comparison</span></a>
</li>
<li class="toclevel-1 tocsection-3">
<a href="#Avoid_ORDER_BY"><span class="tocnumber">3</span> <span class="toctext">Avoid ORDER BY</span></a>
<ul>
<li class="toclevel-2 tocsection-4">
<a href="#Alternative:_denormalize_the_table"><span class="tocnumber">3.1</span> <span class="toctext">Alternative: denormalize the table</span></a>
</li>
<li class="toclevel-2 tocsection-5">
<a href="#Alternative:_multiple_where_clauses"><span class="tocnumber">3.2</span> <span class="toctext">Alternative: multiple where clauses</span></a>
</li>
</ul>
</li>
<li class="toclevel-1 tocsection-6">
<a href="#Beware_bulk_INSERTs_into_a_table_with_a_PRIMARY_KEY"><span class="tocnumber">4</span> <span class="toctext">Beware bulk INSERTs into a table with a PRIMARY KEY</span></a>
</li>
<li class="toclevel-1 tocsection-7">
<a href="#ATTACH"><span class="tocnumber">5</span> <span class="toctext">ATTACH</span></a>
</li>
<li class="toclevel-1 tocsection-8">
<a href="#Get_a_Solid_State_Drive"><span class="tocnumber">6</span> <span class="toctext">Get a Solid State Drive</span></a>
</li>
<li class="toclevel-1 tocsection-9">
<a href="#Use_an_INDEX_for_your_SELECTs.2C_especially_JOINs"><span class="tocnumber">7</span> <span class="toctext">Use an INDEX for your SELECTs, especially JOINs</span></a>
</li>
<li class="toclevel-1 tocsection-10">
<a href="#Use_TRANSACTIONs_for_multiple_INSERT_.2F_UPDATE_.2F_DELETE"><span class="tocnumber">8</span> <span class="toctext">Use TRANSACTIONs for multiple INSERT / UPDATE / DELETE</span></a>
</li>
<li class="toclevel-1 tocsection-11">
<a href="#Use_PRAGMA_page_size_4096"><span class="tocnumber">9</span> <span class="toctext">Use PRAGMA page_size 4096</span></a>
</li>
</ul>
</div>
<h3>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Avoid_LIKE">Avoid LIKE</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Avoid_LIKE" title="Edit section: Avoid_LIKE" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h3>
<ul>
<li>
Like is not performant, as it will search both lowercase and uppercase. You can get around this with PRAGMA case_sensitive_like=OFF;
</li>
<li>
Like does not use an index.
</li>
</ul>
<p>
Consider the following table:
</p>
<pre>
CREATE TABLE tbl1
( id integer NOT NULL PRIMARY KEY
, name varchar(255) NOT NULL
);
CREATE INDEX tbl1__name ON tbl1 (name);
</pre>
<p>
Now, consider the following query:
</p>
<pre>
SELECT id
FROM tbl1
WHERE name LIKE 'a%';
</pre>
<p>
The clause <code>name LIKE 'a%'</code> does not use the index <code>tbl1__name</code>.
</p>
<h3>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Alternative:_Use_comparison">= Alternative: Use comparison</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Alternative:_Use_comparison" title="Edit section: Alternative:_Use_comparison" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h3>
<p>
If the like has a wildcard at the end, and the data is standardized to one case (all lowercase or all uppercase), use an equality instead:
</p>
<pre>
SELECT id
FROM tbl1
WHERE name &gt;= 'a' AND name &lt; 'b';
</pre>
<p>
This uses the index <code>tbl1__name</code> and returns the same data.
</p>
<h3>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Avoid_ORDER_BY">Avoid ORDER BY</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Avoid_ORDER_BY" title="Edit section: Avoid_ORDER_BY" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h3>
<p>
ORDER BY will do an expensive sort operation which may not use an index. This will come into play with multiple-table joins
</p>
<pre>
SELECT t1.id
FROM tbl1 t1
JOIN tbl2 t2 ON t1.id = t2.id
ORDER BY t2.age
;
</pre>
<p>
In most cases, SQLite will only apply one index. In this example, it will be the index for the JOIN. No index gets applied for the score column, even if one is available In some cases, SQLite will actually sort the result-set by the ORDER BY first, before it applies the WHERE.
</p>
<h4>
blog_new_job_
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<span class="mw-headline" id="Alternative:_denormalize_the_table">Alternative: denormalize the table</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Alternative:_denormalize_the_table" title="Edit section: Alternative:_denormalize_the_table" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h4>
<p>
Putting all the columns in one table and building an index across them.
</p>
<h4>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Alternative:_multiple_where_clauses">Alternative: multiple where clauses</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Alternative:_multiple_where_clauses" title="Edit section: Alternative:_multiple_where_clauses" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h4>
<pre>
SELECT t1.id
FROM tbl1 t1
JOIN tbl2 t2 ON t1.id = t2.id
WHERE t2.age &gt; 100 AND t2.age &lt;= 130
;
SELECT t1.id
FROM tbl1 t1
JOIN tbl2 t2 ON t1.id = t2.id
WHERE t2.age &gt; 70 AND t2.age &lt;= 100
;
</pre>
<h3>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Beware_bulk_INSERTs_into_a_table_with_a_PRIMARY_KEY">Beware bulk INSERTs into a table with a PRIMARY KEY</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Beware_bulk_INSERTs_into_a_table_with_a_PRIMARY_KEY" title="Edit section: Beware_bulk_INSERTs_into_a_table_with_a_PRIMARY_KEY" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h3>
<pre>
INSERT INTO
INSERT INTO tbl2 (id, key)
SELECT t1.id
FROM tbl1 t1
JOIN tbl2 t2 ON t1.id = t2.id
WHERE t2.age &gt; 100 AND t2.age &lt;= 130
;
</pre>
<p>
Instead, insert into the table with an ORDER BY
</p>
<h3>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="ATTACH">ATTACH</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=ATTACH" title="Edit section: ATTACH" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h3>
<p>
ATTACH database does not affect performance. There is no difference between the following
</p>
<pre>
SELECT t1.id
FROM tbl1 t1
JOIN tbl2 t2 ON t1.id = t2.id
;
</pre>
<pre>
ATTACH 'db2.sqlite3' AS 'db2';
SELECT t1.id
FROM tbl1 t1
JOIN db2.tbl2 t2 ON t1.id = t2.id
;
</pre>
<h2>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Get_a_Solid_State_Drive">Get a Solid State Drive</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Get_a_Solid_State_Drive" title="Edit section: Get_a_Solid_State_Drive" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h2>
<p>
SQLite does a lot of disk reading and writing
</p>
<h2>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Use_an_INDEX_for_your_SELECTs.2C_especially_JOINs">Use an INDEX for your SELECTs, especially JOINs</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Use_an_INDEX_for_your_SELECTs.2C_especially_JOINs" title="Edit section: Use_an_INDEX_for_your_SELECTs.2C_especially_JOINs" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h2>
<h2>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Use_TRANSACTIONs_for_multiple_INSERT_.2F_UPDATE_.2F_DELETE">Use TRANSACTIONs for multiple INSERT / UPDATE / DELETE</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Use_TRANSACTIONs_for_multiple_INSERT_.2F_UPDATE_.2F_DELETE" title="Edit section: Use_TRANSACTIONs_for_multiple_INSERT_.2F_UPDATE_.2F_DELETE" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h2>
<h2>
blog_new_job_
2017-04-02 16:03:46 +00:00
<span class="mw-headline" id="Use_PRAGMA_page_size_4096">Use PRAGMA page_size 4096</span> <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/wiki/Dev/Sqlite/Tips?action=edit&amp;section_key=Use_PRAGMA_page_size_4096" title="Edit section: Use_PRAGMA_page_size_4096" class="xowa-hover-off">edit</a><span class="mw-editsection-bracket">]</span></span>
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
</h2>
$version_number
2016-09-12 01:53:06 +00:00
'v3.4.2.55'
2016-04-17 15:48:03 +00:00
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'v3.4.2.55'
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'v3.4.2.55'
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'v3.4.2.55'
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