168 lines
6.3 KiB
HTML
168 lines
6.3 KiB
HTML
<!DOCTYPE html>
|
|
<html><head>
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
|
|
<link href="sqlite.css" rel="stylesheet">
|
|
<title>Rowid Tables</title>
|
|
<!-- path= -->
|
|
</head>
|
|
<body>
|
|
<div class=nosearch>
|
|
<a href="index.html">
|
|
<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite" border="0">
|
|
</a>
|
|
<div><!-- IE hack to prevent disappearing logo --></div>
|
|
<div class="tagline desktoponly">
|
|
Small. Fast. Reliable.<br>Choose any three.
|
|
</div>
|
|
<div class="menu mainmenu">
|
|
<ul>
|
|
<li><a href="index.html">Home</a>
|
|
<li class='mobileonly'><a href="javascript:void(0)" onclick='toggle_div("submenu")'>Menu</a>
|
|
<li class='wideonly'><a href='about.html'>About</a>
|
|
<li class='desktoponly'><a href="docs.html">Documentation</a>
|
|
<li class='desktoponly'><a href="download.html">Download</a>
|
|
<li class='wideonly'><a href='copyright.html'>License</a>
|
|
<li class='desktoponly'><a href="support.html">Support</a>
|
|
<li class='desktoponly'><a href="prosupport.html">Purchase</a>
|
|
<li class='search' id='search_menubutton'>
|
|
<a href="javascript:void(0)" onclick='toggle_search()'>Search</a>
|
|
</ul>
|
|
</div>
|
|
<div class="menu submenu" id="submenu">
|
|
<ul>
|
|
<li><a href='about.html'>About</a>
|
|
<li><a href='docs.html'>Documentation</a>
|
|
<li><a href='download.html'>Download</a>
|
|
<li><a href='support.html'>Support</a>
|
|
<li><a href='prosupport.html'>Purchase</a>
|
|
</ul>
|
|
</div>
|
|
<div class="searchmenu" id="searchmenu">
|
|
<form method="GET" action="search">
|
|
<select name="s" id="searchtype">
|
|
<option value="d">Search Documentation</option>
|
|
<option value="c">Search Changelog</option>
|
|
</select>
|
|
<input type="text" name="q" id="searchbox" value="">
|
|
<input type="submit" value="Go">
|
|
</form>
|
|
</div>
|
|
</div>
|
|
<script>
|
|
function toggle_div(nm) {
|
|
var w = document.getElementById(nm);
|
|
if( w.style.display=="block" ){
|
|
w.style.display = "none";
|
|
}else{
|
|
w.style.display = "block";
|
|
}
|
|
}
|
|
function toggle_search() {
|
|
var w = document.getElementById("searchmenu");
|
|
if( w.style.display=="block" ){
|
|
w.style.display = "none";
|
|
} else {
|
|
w.style.display = "block";
|
|
setTimeout(function(){
|
|
document.getElementById("searchbox").focus()
|
|
}, 30);
|
|
}
|
|
}
|
|
function div_off(nm){document.getElementById(nm).style.display="none";}
|
|
window.onbeforeunload = function(e){div_off("submenu");}
|
|
/* Disable the Search feature if we are not operating from CGI, since */
|
|
/* Search is accomplished using CGI and will not work without it. */
|
|
if( !location.origin || !location.origin.match || !location.origin.match(/http/) ){
|
|
document.getElementById("search_menubutton").style.display = "none";
|
|
}
|
|
/* Used by the Hide/Show button beside syntax diagrams, to toggle the */
|
|
function hideorshow(btn,obj){
|
|
var x = document.getElementById(obj);
|
|
var b = document.getElementById(btn);
|
|
if( x.style.display!='none' ){
|
|
x.style.display = 'none';
|
|
b.innerHTML='show';
|
|
}else{
|
|
x.style.display = '';
|
|
b.innerHTML='hide';
|
|
}
|
|
return false;
|
|
}
|
|
</script>
|
|
</div>
|
|
|
|
|
|
<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>
|
|
|