212 lines
7.4 KiB
HTML
212 lines
7.4 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>The SQLITE_DBPAGE Virtual Table</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>
|
|
<div class=fancy>
|
|
<div class=nosearch>
|
|
<div class="fancy_title">
|
|
The SQLITE_DBPAGE Virtual Table
|
|
</div>
|
|
</div>
|
|
|
|
|
|
|
|
|
|
<h1 id="overview"><span>1. </span>Overview</h1>
|
|
|
|
<p>
|
|
The SQLITE_DBPAGE extension implements an <a href="vtab.html#epoonlyvtab">eponymous-only virtual table</a> that
|
|
provides direct access to the underlying database file by interacting
|
|
with the pager. SQLITE_DBPAGE is capable of both reading and writing any
|
|
page of the database. Because interaction is through the pager layer, all
|
|
changes are transactional.
|
|
</p>
|
|
|
|
<p>
|
|
<b>Warning:</b> writing to the SQLITE_DBPAGE virtual table can very easily
|
|
cause unrecoverably database corruption. Do not allow untrusted components
|
|
to access the SQLITE_DBPAGE table. Use appropriate care while using the
|
|
SQLITE_DBPAGE table. Back up important data prior to experimenting with the
|
|
SQLITE_DBPAGE table. Writes to the SQLITE_DBPAGE virtual table are
|
|
disabled when the <a href="c3ref/c_dbconfig_defensive.html#sqlitedbconfigdefensive">SQLITE_DBCONFIG_DEFENSIVE</a> flag is set.
|
|
|
|
</p><p>
|
|
The SQLITE_DBPAGE extension is included in the <a href="amalgamation.html">amalgamation</a> though
|
|
it is disabled
|
|
by default. Use the <a href="compile.html#enable_dbpage_vtab">SQLITE_ENABLE_DBPAGE_VTAB</a> compile-time option to enable
|
|
the SQLITE_DBPAGE extension. The SQLITE_DBPAGE extension makes use of
|
|
unpublished internal interfaces and is not run-time loadable. The only way
|
|
to add SQLITE_DBPAGE to an application is to compile it in using the
|
|
<a href="compile.html#enable_dbpage_vtab">SQLITE_ENABLE_DBPAGE_VTAB</a> compile-time option.
|
|
</p>
|
|
|
|
<p>
|
|
The SQLITE_DBPAGE extension is enabled in default builds
|
|
of the <a href="cli.html">command-line shell</a>.
|
|
|
|
</p><h1 id="usage"><span>2. </span>Usage</h1>
|
|
|
|
<p>
|
|
The SQLITE_DBPAGE virtual table read/write table that provides direct
|
|
access to the underlying disk file on a page-by-page basis. The
|
|
virtual table appears to have a schema like this:
|
|
|
|
</p><div class="codeblock"><pre>CREATE TABLE sqlite_dbpage(
|
|
pgno INTEGER PRIMARY KEY,
|
|
data BLOB
|
|
);
|
|
</pre></div>
|
|
|
|
<p>
|
|
An SQLite database file is divided into pages.
|
|
The first page is 1, the second page is 2, and so forth.
|
|
There is no page 0.
|
|
Every page is the same size.
|
|
The size of every page is a power of 2 between 512 and 65536.
|
|
See the <a href="fileformat2.html">file format</a> documentation for further details.
|
|
|
|
</p><p>
|
|
The SQLITE_DBPAGE table allows an application to view or replace the
|
|
raw binary content of each page of the database file.
|
|
No attempt is made to interpret the content of the page.
|
|
Content is returned byte-for-byte as it appears on disk.
|
|
|
|
</p><p>
|
|
The SQLITE_DBPAGE table has one row for each page in the database file.
|
|
SQLITE_DBPAGE allows pages to be read or to be overwritten.
|
|
However the size of the database file cannot be changed. It is not
|
|
possible to change the number of rows in the SQLITE_DBPAGE table by
|
|
running DELETE or INSERT operations against that table.
|
|
|
|
</p><h2 id="using_sqlite_dbpage_on_attach_ed_databases"><span>2.1. </span>Using SQLITE_DBPAGE On ATTACH-ed Databases</h2>
|
|
|
|
<p>
|
|
The SQLITE_DBPAGE table schema shown above is incomplete. There is
|
|
a third <a href="vtab.html#hiddencol">hidden column</a> named "schema" that determines which
|
|
<a href="lang_attach.html">ATTACH-ed database</a> should be read or written. Because
|
|
the "schema" column is hidden, it can be used as a parameter when
|
|
SQLITE_DBPAGE is invoked as a <a href="vtab.html#tabfunc2">table-valued function</a>.
|
|
|
|
</p><p>
|
|
For example, suppose an additional database is attached to the
|
|
database connection using a statement like this:
|
|
|
|
</p><div class="codeblock"><pre>ATTACH 'auxdata1.db' AS aux1;
|
|
</pre></div>
|
|
|
|
<p>
|
|
Then to read the first page of that database file, one merely runs:
|
|
|
|
</p><div class="codeblock"><pre>SELECT data FROM sqlite_dbpage('aux1') WHERE pgno=1;
|
|
</pre></div>
|
|
|
|
<p>
|
|
If the "schema" is omitted, it defaults to the primary database
|
|
(usually called 'main', unless renamed using <a href="c3ref/c_dbconfig_defensive.html#sqlitedbconfigmaindbname">SQLITE_DBCONFIG_MAINDBNAME</a>).
|
|
Hence, the following two queries are normally equivalent:
|
|
|
|
</p><div class="codeblock"><pre>SELECT data FROM sqlite_dbpage('main') WHERE pgno=1;
|
|
SELECT data FROM sqlite_dbpage WHERE pgno=1;
|
|
</pre></div>
|
|
|
|
<p>
|
|
The SQLITE_DBPAGE table can participate in a join just like any other
|
|
table. Hence, to see the content of the first page to all connected
|
|
database files, one might run a statement like this:
|
|
|
|
</p><div class="codeblock"><pre>SELECT dbpage.data, dblist.name
|
|
FROM pragma_database_list AS dblist
|
|
JOIN sqlite_dbpage(dblist.name) AS dbpage
|
|
WHERE dbpage.pgno=1;
|
|
</pre></div>
|
|
|