Adding upstream version 3.40.1.upstream/3.40.1 upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
commit: 18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree: 17b438b680ed45a996d7b59951e6aa34023783f2 /www/deterministic.html
parent: Initial commit. (diff)
download: sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz
sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip
1 files changed, 255 insertions, 0 deletions
diff --git a/www/deterministic.html b/www/deterministic.html
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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>Deterministic SQL Functions</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">
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+<form method="GET" action="search">
+<select name="s" id="searchtype">
+<option value="d">Search Documentation</option>
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+</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";
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+/* 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';
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+return false;
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+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;
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+document.body.onmousemove=function(){
+antiRobot |= 2;
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+setTimeout(function(){
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+antiRobotDefense();
+</script>
+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+Deterministic SQL Functions
+</div>
+</div>
+
+
+
+
+
+<h1 id="overview"><span>1. </span>Overview</h1>
+
+<p>
+SQL functions in SQLite can be either "deterministic" or "non-deterministic".
+
+</p><p>
+A deterministic function always gives the same answer when it has
+the same inputs.  Most built-in SQL functions in SQLite are
+deterministic.  For example, the <a href="lang_corefunc.html#abs">abs(X)</a> function always returns
+the same answer as long as its input X is the same.
+
+</p><p>
+Non-deterministic functions might give different answers on each
+invocation, even if the arguments are always the same.  The following
+are examples of non-deterministic functions:
+
+</p><ul>
+<li> <a href="lang_corefunc.html#random">random()</a>
+</li><li> <a href="lang_corefunc.html#changes">changes()</a>
+</li><li> <a href="lang_corefunc.html#last_insert_rowid">last_insert_rowid()</a>
+</li><li> <a href="c3ref/libversion.html">sqlite3_version()</a>
+</li></ul>
+
+<p>
+The <a href="lang_corefunc.html#random">random()</a> function is obviously non-deterministic because it gives
+a different answer every time it is invoked.  The answers from <a href="lang_corefunc.html#changes">changes()</a>
+and <a href="lang_corefunc.html#last_insert_rowid">last_insert_rowid()</a> depend on prior SQL statements, and so they
+are also non-deterministic. The
+<a href="c3ref/libversion.html">sqlite3_version()</a> function is mostly constant, but it can change when
+SQLite is upgraded, and so even though it always returns the same answer
+for any particular session, because it can change answers across sessions
+it is still considered non-deterministic.
+
+
+</p><h1 id="restrictions_on_the_use_of_non_deterministic_functions"><span>2. </span>Restrictions on the use of non-deterministic functions</h1>
+
+<p>
+There are some contexts in SQLite that do not allow the use of
+non-deterministic functions:
+
+</p><ul>
+<li>In the expression of a <a href="lang_createtable.html#ckconst">CHECK constraint</a>.
+</li><li>In the WHERE clause of a <a href="partialindex.html">partial index</a>.
+</li><li>In an expression used as part of an <a href="expridx.html">expression index</a>.
+</li><li>In the expression of a <a href="gencol.html">generated column</a>.
+</li></ul>
+
+<p>
+In the cases above, the values returned by the function affects the
+information stored in the database file.  The values of functions
+in CHECK constraints determines which entries are valid for a table,
+and functions in the WHERE clause of a partial index or in an index on
+an expression compute values stored in the index b-tree.
+If any of these functions later returns a different
+value, then the database might no longer be well-formed.  
+Hence, to avoid database corruption,
+only deterministic functions can be used in the contexts
+above.
+
+<a name="dtexception"></a>
+
+</p><h1 id="special_case_processing_for_date_time_functions"><span>3. </span>Special-case Processing For Date/Time Functions</h1>
+
+<p>
+The built-in <a href="lang_datefunc.html">date and time functions</a> of SQLite are a special case.
+These functions are usually considered deterministic.  However, if
+these functions use the string "now" as the date, or if they use
+the <a href="lang_datefunc.html#localtime">localtime modifier</a> or the <a href="lang_datefunc.html#localtime">utc modifier</a>, then they are
+considered non-deterministic.  Because the function inputs are
+not necessarily known until run-time, the date/time functions will
+throw an exception if they encounter any of the non-deterministic
+features in a context where only deterministic functions are allowed.
+
+</p><p>
+Prior to SQLite 3.20.0 (2017-08-01) all date/time functions were
+always considered non-deterministic.  The ability for date/time functions
+to be deterministic sometimes and non-deterministic at other times,
+depending on their arguments, was added for the 3.20.0 release.
+
+</p><h2 id="bug_fix_in_version_3_35_2"><span>3.1. </span>Bug fix in version 3.35.2</h2>
+
+<p>
+When the enhancement was made to SQLite 3.20.0 such that date/time
+functions would be considered deterministic as they do not depend
+on the current time, one case was overlooked:
+Many of the date/time functions can be called
+with no arguments at all.  These no-argument date/time functions
+behave as if they had a single "<tt>'now'</tt>" argument.
+Thus "<tt>datetime()</tt>" and
+"<tt>datetime('now')</tt>" both yield the current date and time.
+However, only the second form was recognized as non-deterministic.
+This meant that developers could sneak the non-deterministic
+"<tt>datetime()</tt>" form into CHECK constraints, index
+expressions, generated column expressions, and similar places
+where non-deterministic functions make no sense.
+This oversight was fixed in version 3.35.2 (2021-03-17).
+However, there may be legacy databases in circulation that were created
+by SQLite version 3.20.0 through 3.35.1 that have non-deterministic
+date/time functions in their schemas.
+
+</p><h1 id="application_defined_deterministic_functions"><span>4. </span>Application-defined deterministic functions</h1>
+
+<p>
+By default, <a href="appfunc.html">application-defined SQL functions</a> are considered to
+be non-deterministic.  However, if the 4th parameter to
+<a href="c3ref/create_function.html">sqlite3_create_function_v2()</a> is OR-ed with 
+<a href="c3ref/c_deterministic.html#sqlitedeterministic">SQLITE_DETERMINISTIC</a>, then SQLite will treat that function as if it
+were deterministic.
+
+</p><p>
+Note that if a non-deterministic function is tagged with
+<a href="c3ref/c_deterministic.html#sqlitedeterministic">SQLITE_DETERMINISTIC</a> and if that function ends up being used in
+the WHERE clause of a <a href="partialindex.html">partial index</a> or in an
+<a href="expridx.html">expression index</a>, then when the function begins to return different
+answers, the associated index may become corrupt.  If an SQL function
+is nearly deterministic (which is to say, if it only rarely changes,
+like <a href="lang_corefunc.html#sqlite_version">sqlite_version()</a>) and it is used in an index that becomes
+corrupt, the corruption can be fixed by running <a href="lang_reindex.html">REINDEX</a>.
+
+</p><p>
+The interfaces necessary to construct a function that is sometimes
+deterministic and sometimes non-deterministic depending on their
+inputs, such as the built-in date/time functions, are not published.
+Generic <a href="appfunc.html">application-defined SQL functions</a> must
+be always deterministic or always non-deterministic.
+</p><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/deterministic.in?m=72aa24619c4616127">2021-06-17 16:11:09</a> UTC </small></i></p>
+
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
commit	18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree	17b438b680ed45a996d7b59951e6aa34023783f2 /www/deterministic.html
parent	Initial commit. (diff)
download	sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip