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- <h2 align="center">SQL As Understood By SQLite</h2></a><h1>ANALYZE</h1><h4><a href="syntaxdiagrams.html#analyze-stmt">analyze-stmt:</a></h4><blockquote> <img alt="syntax diagram analyze-stmt" src="images/syntax/analyze-stmt.gif"></img> </blockquote>
- <p>The ANALYZE command gathers statistics about indices and stores them
- in a special tables in the database where the query optimizer can use
- them to help make better index choices.
- If no arguments are given, all indices in all attached databases are
- analyzed. If a database name is given as the argument, all indices
- in that one database are analyzed. If the argument is a table name,
- then only indices associated with that one table are analyzed.</p>
- <p>The default implementation stores all statistics in a single
- table named <b>sqlite_stat1</b>. If SQLite is compiled with the
- <a href="compile.html#enable_stat2">SQLITE_ENABLE_STAT2</a> option, then additional histogram data is
- collected and stored in <b>sqlite_stat2</b>.
- Future enhancements may create
- additional tables with the same name pattern except with the "1"
- or "2" changed to a different digit.</p>
- <p>The <a href="lang_droptable.html">DROP TABLE</a> command does
- not work on the <b>sqlite_stat1</b> or <b>sqlite_stat2</b> tables,
- but all the content of those tables can be queried using <a href="lang_select.html">SELECT</a>
- and can be deleted, augmented, or modified using the <a href="lang_delete.html">DELETE</a>,
- <a href="lang_insert.html">INSERT</a>, and <a href="lang_update.html">UPDATE</a> commands.
- Appropriate care should be used when changing the content of the statistics
- tables as invalid content can cause SQLite to select inefficient
- query plans. Generally speaking, one should not modify the content of
- the statistics tables by any mechanism other than invoking the
- ANALYZE command.</p>
- <p>Statistics gathered by ANALYZE are <u>not</u> automatically updated as
- the content of the database changes. If the content of the database
- changes significantly, or if the database schema changes, then one should
- consider rerunning the ANALYZE command in order to update the statistics.</p>
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