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TYPES </td>
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<span id="nsrTitle">SQLite Language Reference Documentation</span>
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<h1 class="heading">
SQL As Understood By SQLite</h1>
<h4>
TYPES</h4>
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<i><font color="#ff3434">sql-statement</font></i> ::=</td>
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<b><font color="#2c2cf0">TYPES </font></b>[<b><font color="#2c2cf0"></font></b><i><font
color="#ff3434">datatype name</font></i><b><font color="#2c2cf0"></font></b>][,<b><font color="#2c2cf0"></font></b><i><font
color="#ff3434">datatype name</font></i><b><font color="#2c2cf0"></font></b>][,<b><font color="#2c2cf0"></font></b><i><font
color="#ff3434">datatype
name</font></i><b><font color="#2c2cf0"></font></b>][,<b><font color="#2c2cf0"></font></b><i><font
color="#ff3434">...</font></i>] ; <em><span style="color: #ff3434">select stmt</span></em></td>
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<p>
The VACUUM command is an SQLite extension modeled after a similar command found
in PostgreSQL. If VACUUM is invoked with the name of a table or index then it is
suppose to clean up the named table or index. In version 1.0 of SQLite, the VACUUM
command would invoke <b>gdbm_reorganize()</b> to clean up the backend database file.</p>
<p>
VACUUM became a no-op when the GDBM backend was removed from SQLITE in version 2.0.0.
VACUUM was reimplemented in version 2.8.1. The index or table name argument is now
ignored.
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<p>
When an object (table, index, or trigger) is dropped from the database, it leaves
behind empty space. This makes the database file larger than it needs to be, but
can speed up inserts. In time inserts and deletes can leave the database file structure
fragmented, which slows down disk access to the database contents. The VACUUM command
cleans the main database by copying its contents to a temporary database file and
reloading the original database file from the copy. This eliminates free pages,
aligns table data to be contiguous, and otherwise cleans up the database file structure.
It is not possible to perform the same process on an attached database file.</p>
<p>
This command will fail if there is an active transaction. This command has no effect
on an in-memory database.</p>
<p>
As of SQLite version 3.1, an alternative to using the VACUUM command is auto-vacuum
mode, enabled using the <a href="pragma.html#pragma_auto_vacuum">auto_vacuum pragma</a>.</p>
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