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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 17:28:19 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 17:28:19 +0000
commit18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree17b438b680ed45a996d7b59951e6aa34023783f2 /www/unionvtab.html
parentInitial commit. (diff)
downloadsqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz
sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip
Adding upstream version 3.40.1.upstream/3.40.1upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<!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 UNION 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;
+}
+var antiRobot = 0;
+function antiRobotGo(){
+if( antiRobot!=3 ) return;
+antiRobot = 7;
+var j = document.getElementById("mtimelink");
+if(j && j.hasAttribute("data-href")) j.href=j.getAttribute("data-href");
+}
+function antiRobotDefense(){
+document.body.onmousedown=function(){
+antiRobot |= 2;
+antiRobotGo();
+document.body.onmousedown=null;
+}
+document.body.onmousemove=function(){
+antiRobot |= 2;
+antiRobotGo();
+document.body.onmousemove=null;
+}
+setTimeout(function(){
+antiRobot |= 1;
+antiRobotGo();
+}, 100)
+antiRobotGo();
+}
+antiRobotDefense();
+</script>
+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+The UNION Virtual Table
+</div>
+</div>
+
+
+
+
+
+<ol>
+<li value="100"><p>
+The UNION virtual table (hereafter: "union-vtab")
+is a <a href="vtab.html">virtual table</a> that makes multiple independent
+<a href="rowidtable.html">rowid tables</a> tables look like a single large table.
+
+</p></li><li value="110"><p>
+The tables that participate in a union-vtab can be in the same
+database file, or they can be in separate databases files that
+are <a href="lang_attach.html">ATTACH</a>-ed to the same database connection.
+
+</p></li><li value="120"><p>
+The union-vtab is not built into SQLite.
+Union-vtab is a <a href="loadext.html">loadable extension</a>.
+The source code for union-vtab is contained in a single file located at
+<a href="https://sqlite.org/src/file/ext/misc/unionvtab.c">ext/misc/unionvtab.c</a>
+in the SQLite source tree.
+
+</p></li><li value="200"><p>
+A new union-vtab instance is created as follows:
+
+</p><blockquote>
+<b>CREATE VIRTUAL TABLE temp.</b><i>tabname</i> <b>USING unionvtab(</b><i>query</i><b>);</b>
+</blockquote>
+
+</li><li value="210"><p>
+Every union-vtab must be in the TEMP namespace. Hence, the "<b>temp.</b>"
+prior to <i>tabname</i> is required. Only the union-vtab itself is required
+to be in the TEMP namespace - the individual tables that are being unioned
+can be any <a href="lang_attach.html">ATTACH</a>-ed database.
+
+</p></li><li value="220"><p>
+The <i>query</i> in the CREATE VIRTUAL TABLE statement for a union-vtab
+must be a well-formed SQL query that returns four columns and an
+arbitrary number of rows. Each row in the result of the <i>query</i>
+represents a single table that is to participate in the union.
+</p><ol>
+<li value="221'">
+The first column is the schema name for the database that contains
+the tables. Examples: "main", "zone512".
+</li><li value="222'">
+The second column is the name of the table.
+</li><li value="223'">
+The third column is the minimum value for any rowid in the table.
+</li><li value="224'">
+The fourth column is the maximum value of any rowid in the table.
+</li></ol>
+
+</li><li value="230"><p>
+The <i>query</i> for the CREATE VIRTUAL TABLE statement of a union-vtab
+can be either a <a href="lang_select.html">SELECT</a> statement or a <a href="lang_select.html#values">VALUES clause</a>.
+
+</p></li><li value="240"><p>
+The <i>query</i> is run once when the CREATE VIRTUAL TABLE statement is
+first encountered and the results of that one run are used for all subsequent
+access to the union-vtab. If the results of <i>query</i> change, then
+the union-vtab should be <a href="lang_droptable.html">DROP</a>-ed and recreated in order
+to cause the <i>query</i> to be run again.
+
+</p></li><li value="250"><p>
+There must be no overlap in the bands of rowids for the various tables
+in a union-vtab.
+
+</p></li><li value="260"><p>
+All tables that participate in a union-vtab must have identical
+CREATE TABLE definitions, except that the names of the tables can be different.
+
+</p></li><li value="270"><p>
+All tables that participate in a union-vtab must be <a href="rowidtable.html">rowid tables</a>.
+
+</p></li><li value="280"><p>
+The column names and definitions for <i>tabname</i> will be the same as
+the underlying tables. An application can access <i>tabname</i> just like
+it was one of the real underlying tables.
+
+</p></li><li value="290"><p>
+No table in a union-vtab may contain entries that are outside of the
+rowid bounds established by the <i>query</i> in the CREATE VIRTUAL TABLE
+statement.
+
+</p></li><li value="300"><p>
+The union-vtab shall optimize access to the underlying real tables
+when the constraints on the query are among forms shown below.
+Other kinds of constraints may be optimized in the future, but only
+these constraints are optimized in the initial implementation.
+</p><ul>
+<li> <b>rowid=$id</b>
+</li><li> <b>rowid IN</b> <i>query-or-list</i>
+</li><li> <b>rowid BETWEEN $lwr AND $upr</b>
+</li></ul>
+<p>
+Other kinds of constraints may be used and will work, but other
+constraints will be checked individually for each row and will not
+be optimized (at least not initially).
+All constraint checking is completely automatic regardless of whether
+or not optimization occurs. The optimization referred to in this bullet point
+is a performance consideration only. The same result is obtained
+regardless of whether or not the query is optimized.
+
+</p></li><li value="310"><p>
+The union-vtab is read-only. Support for writing may be added at a later
+time, but writing is not a part of the initial implementation.
+
+</p></li><li value="320"><p>
+<i>Nota bene:</i>
+The <a href="c3ref/blob_open.html">sqlite3_blob_open()</a> interface does <u>not</u> work for a union-vtab.
+BLOB content must be read from the union-vtab using ordinary SQL statements.
+</p></li></ol>
+<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/unionvtab.in?m=46e606d9d8ba1f99e">2017-07-21 19:12:49</a> UTC </small></i></p>
+
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-19 02:30:28 +0000