1
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
3
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
4
<title>SQLite Query Language: INDEXED BY</title>
5
<style type="text/css">
8
font-family: Verdana, sans-serif;
13
a:visited { color: #734559 }
15
.logo { position:absolute; margin:3px; }
31
.toolbar a { color: white; text-decoration: none; padding: 6px 12px; }
32
.toolbar a:visited { color: white; }
33
.toolbar a:hover { color: #044a64; background: white; }
35
.content { margin: 5%; }
36
.content dt { font-weight:bold; }
37
.content dd { margin-bottom: 25px; margin-left:20%; }
38
.content ul { padding:0px; padding-left: 15px; margin:0px; }
41
.se { background: url(images/se.gif) 100% 100% no-repeat #044a64}
42
.sw { background: url(images/sw.gif) 0% 100% no-repeat }
43
.ne { background: url(images/ne.gif) 100% 0% no-repeat }
44
.nw { background: url(images/nw.gif) 0% 0% no-repeat }
46
/* Things for "fancyformat" documents start here. */
47
.fancy img+p {font-style:italic}
48
.fancy .codeblock i { color: darkblue; }
49
.fancy h1,.fancy h2,.fancy h3,.fancy h4 {font-weight:normal;color:#044a64}
50
.fancy h2 { margin-left: 10px }
51
.fancy h3 { margin-left: 20px }
52
.fancy h4 { margin-left: 30px }
53
.fancy th {white-space:nowrap;text-align:left;border-bottom:solid 1px #444}
54
.fancy th, .fancy td {padding: 0.2em 1ex; vertical-align:top}
55
.fancy #toc a { color: darkblue ; text-decoration: none }
56
.fancy .todo { color: #AA3333 ; font-style : italic }
57
.fancy .todo:before { content: 'TODO:' }
58
.fancy p.todo { border: solid #AA3333 1px; padding: 1ex }
59
.fancy img { display:block; }
60
.fancy :link:hover, .fancy :visited:hover { background: wheat }
61
.fancy p,.fancy ul,.fancy ol { margin: 1em 5ex }
62
.fancy li p { margin: 1em 0 }
63
/* End of "fancyformat" specific rules. */
69
<div><!-- container div to satisfy validator -->
72
<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite Logo"
74
<div><!-- IE hack to prevent disappearing logo--></div>
75
<div class="tagline">Small. Fast. Reliable.<br>Choose any three.</div>
77
<table width=100% style="clear:both"><tr><td>
78
<div class="se"><div class="sw"><div class="ne"><div class="nw">
79
<table width=100% style="padding:0;margin:0;cell-spacing:0"><tr>
82
<a href="about.html">About</a>
83
<a href="sitemap.html">Sitemap</a>
84
<a href="docs.html">Documentation</a>
85
<a href="download.html">Download</a>
86
<a href="copyright.html">License</a>
87
<a href="news.html">News</a>
88
<a href="support.html">Support</a>
91
gMsg = "Search SQLite Docs..."
92
function entersearch() {
93
var q = document.getElementById("q");
94
if( q.value == gMsg ) { q.value = "" }
95
q.style.color = "black"
96
q.style.fontStyle = "normal"
98
function leavesearch() {
99
var q = document.getElementById("q");
100
if( q.value == "" ) {
102
q.style.color = "#044a64"
103
q.style.fontStyle = "italic"
108
<div style="padding:0 1em 0px 0;white-space:nowrap">
109
<form name=f method="GET" action="http://www.sqlite.org/search">
110
<input id=q name=q type=text
111
onfocus="entersearch()" onblur="leavesearch()" style="width:24ex;padding:1px 1ex; border:solid white 1px; font-size:0.9em ; font-style:italic;color:#044a64;" value="Search SQLite Docs...">
112
<input type=submit value="Go" style="border:solid white 1px;background-color:#044a64;color:white;font-size:0.9em;padding:0 1ex">
116
</div></div></div></div>
118
<div class=startsearch></div>
120
<h1 align="center">SQL As Understood By SQLite</h1><p><a href="lang.html">[Top]</a></p><h2>INDEXED BY</h2>
121
<p>The INDEXED BY phrase is an SQL extension found only in SQLite which can
122
be used to verify that the correct indices are being used on a <a href="lang_delete.html">DELETE</a>,
123
<a href="lang_select.html">SELECT</a>, or <a href="lang_update.html">UPDATE</a> statement.
124
The INDEXED BY phrase always follows the name of a table that SQLite will
125
be reading. The INDEXED BY phrase can be seen in the following syntax
128
<h4><a href="syntaxdiagrams.html#qualified-table-name">qualified-table-name:</a></h4><blockquote> <img alt="syntax diagram qualified-table-name" src="images/syntax/qualified-table-name.gif"></img> </blockquote>
129
<h4><a href="syntaxdiagrams.html#single-source">single-source:</a></h4><blockquote> <img alt="syntax diagram single-source" src="images/syntax/single-source.gif"></img> </blockquote>
132
<p>The "INDEXED BY index-name" clause specifies that the named index
133
must be used in order to look up values on the preceding table.
134
If index-name does not exist or cannot be used for the query, then
135
the preparation of the SQL statement fails.
136
The "NOT INDEXED" clause specifies that no index shall be used when
137
accessing the preceding table, including implied indices create by
138
UNIQUE and PRIMARY KEY constraints. However, the INTEGER PRIMARY KEY
139
can still be used to look up entries even when "NOT INDEXED" is specified.</p>
141
<p>Some SQL database engines provide non-standard "hint" mechanisms which
142
can be used to give the query optimizer clues about what indices it should
143
use for a particular statement. The INDEX BY clause of SQLite is
144
<em>not</em> a hinting mechanism and it should not be used as such.
145
The INDEXED BY clause does not give the optimizer hints about which index
146
to use; it gives the optimizer a requirement of which index to use.
147
If the query optimizer is unable to use the index specified by the
148
INDEX BY clause, then the query will fail with an error.</p>
150
<p>The INDEXED BY clause is <em>not</em> intended for use in tuning
151
the performance of a query. The intent of the INDEXED BY clause is
152
to raise a run-time error if a schema change, such as dropping or
153
creating an index, causes the query plan for a time-sensitive query
154
to change. The INDEXED BY clause is designed to help detect
155
undesirable query plan changes during regression testing.
156
Developers are admonished to omit all use of INDEXED BY during
157
application design, implementation, testing, and tuning. If
158
INDEXED BY is to be used at all, it should be inserted at the very
159
end of the development process when "locking down" a design.</p>
163
<p>The <a href="c3ref/stmt_status.html">sqlite3_stmt_status()</a> C/C++ interface together with the
164
<a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusfullscanstep">SQLITE_STMTSTATUS_FULLSCAN_STEP</a> and <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatussort">SQLITE_STMTSTATUS_SORT</a> verbs
165
can be used to detect at run-time when an SQL statement is not
166
making effective use of indices. Many applications may prefer to
167
use the <a href="c3ref/stmt_status.html">sqlite3_stmt_status()</a> interface to detect index misuse
168
rather than the INDEXED BY phrase described here.</p>
170
<DIV class="pdf_section">
added
removed
lang_indexedby.html
