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<h1 align="center">Rowid Tables</h1>
<h2>1.0 Definition</h2>
<p>A "rowid table" is any table in an SQLite schema that
<ul>
<li>is <em>not</em> a <a href="vtab.html">virtual table</a>, and
<li>is <em>not</em> a <a href="withoutrowid.html">WITHOUT ROWID</a> table.
</ul>
Most tables in a typical SQLite database schema are rowid tables.
<p>Rowid tables are distinguished by the fact that they all have
a unique, non-NULL, signed 64-bit integer <a href="lang_createtable.html#rowid">rowid</a> that is used as
the access key for the data in the underlying <a href="fileformat2.html#btree">B-tree</a> storage engine.
<h2>2.0 Quirks</h2>
<ul>
<li><p>
The <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> of a rowid table (if there is one) is usually not the
true primary key for the table, in the sense that it is not the unique
key used by the underlying <a href="fileformat2.html#btree">B-tree</a> storage engine. The exception to
this rule is when the rowid table declares an <a href="lang_createtable.html#rowid">INTEGER PRIMARY KEY</a>.
In the exception, the INTEGER PRIMARY KEY becomes an alias for the
<a href="lang_createtable.html#rowid">rowid</a>.
<li><p>
The true primary key for a rowid table (the value that is used as the
key to look up rows in the underlying <a href="fileformat2.html#btree">B-tree</a> storage engine)
is the <a href="lang_createtable.html#rowid">rowid</a>.
<li><p>
The PRIMARY KEY constraint for a rowid table (as long as it is not
the true primary key or INTEGER PRIMARY KEY) is really the same thing
as a <a href="lang_createtable.html#uniqueconst">UNIQUE constraint</a>. Because it is not a true primary key,
columns of the PRIMARY KEY are allowed to be NULL, in violation of
all SQL standards.
<li><p>
The <a href="lang_createtable.html#rowid">rowid</a> of a rowid table can be accessed (or changed) by reading or
writing to any of the "rowid" or "oid" or "_rowid_" columns. Except,
if there is a declared columns in the table that use those
special names, then those names refer to the declared columns, not to
the underlying <a href="lang_createtable.html#rowid">rowid</a>.
<li><p>
Access to records via <a href="lang_createtable.html#rowid">rowid</a> is highly optimized and very fast.
<li><p>
If the <a href="lang_createtable.html#rowid">rowid</a> is not aliased by <a href="lang_createtable.html#rowid">INTEGER PRIMARY KEY</a> then it is not
persistent and might change. In particular the <a href="lang_vacuum.html">VACUUM</a> command will
change rowids for tables that do not declare an INTEGER PRIMARY KEY.
Therefore, applications should not normally access the rowid directly,
but instead use an INTEGER PRIMARY KEY.
<li><p>
In the underlying <a href="fileformat2.html">file format</a>, each rowid is stored as a
<a href="fileformat2.html#varint">variable-length integer</a>. That means that small non-negative
rowid values take up less disk space than large or negative
rowid values.
<li><p>
All of the complications above (and others not mentioned here)
arise from the need to preserve backwards
compatibility for the hundreds of billions of SQLite database files in
circulation. In a perfect world, there would be no such thing as a "rowid"
and all tables would following the standard semantics implemented as
<a href="withoutrowid.html">WITHOUT ROWID</a> tables, only without the extra "WITHOUT ROWID" keywords.
Unfortunately, life is messy. The designer of SQLite offers his
sincere apology for the current mess.
</ul>
<p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/rowidtable.in?m=d768bc62edee4f842">2018-04-12 15:31:42</a> UTC </small></i></p>
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