302 lines
13 KiB
HTML
302 lines
13 KiB
HTML
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<title>CREATE INDEX</title>
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CREATE INDEX
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</div>
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</div>
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<h1 id="syntax"><span>1. </span>Syntax</h1>
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<p><b><a href="syntax/create-index-stmt.html">create-index-stmt:</a></b>
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<button id='x1323' onclick='hideorshow("x1323","x1324")'>hide</button></p>
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<div id='x1324' class='imgcontainer'>
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<img alt="syntax diagram create-index-stmt" src="images/syntax/create-index-stmt.gif" />
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<p><b><a href="syntax/expr.html">expr:</a></b>
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<button id='x1325' onclick='hideorshow("x1325","x1326")'>show</button></p>
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<div id='x1326' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram expr" src="images/syntax/expr.gif" />
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<p><b><a href="syntax/filter-clause.html">filter-clause:</a></b>
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<button id='x1327' onclick='hideorshow("x1327","x1328")'>show</button></p>
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<div id='x1328' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram filter-clause" src="images/syntax/filter-clause.gif" />
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</div>
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<p><b><a href="syntax/literal-value.html">literal-value:</a></b>
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<button id='x1329' onclick='hideorshow("x1329","x1330")'>show</button></p>
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<div id='x1330' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram literal-value" src="images/syntax/literal-value.gif" />
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</div>
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<p><b><a href="syntax/over-clause.html">over-clause:</a></b>
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<button id='x1331' onclick='hideorshow("x1331","x1332")'>show</button></p>
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<div id='x1332' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram over-clause" src="images/syntax/over-clause.gif" />
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<p><b><a href="syntax/frame-spec.html">frame-spec:</a></b>
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<button id='x1333' onclick='hideorshow("x1333","x1334")'>show</button></p>
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<div id='x1334' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram frame-spec" src="images/syntax/frame-spec.gif" />
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</div>
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<p><b><a href="syntax/ordering-term.html">ordering-term:</a></b>
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<button id='x1335' onclick='hideorshow("x1335","x1336")'>show</button></p>
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<div id='x1336' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram ordering-term" src="images/syntax/ordering-term.gif" />
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</div>
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</div>
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<p><b><a href="syntax/raise-function.html">raise-function:</a></b>
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<button id='x1337' onclick='hideorshow("x1337","x1338")'>show</button></p>
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<div id='x1338' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram raise-function" src="images/syntax/raise-function.gif" />
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</div>
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<p><b><a href="syntax/select-stmt.html">select-stmt:</a></b>
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<button id='x1339' onclick='hideorshow("x1339","x1340")'>show</button></p>
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<div id='x1340' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram select-stmt" src="images/syntax/select-stmt.gif" />
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<p><b><a href="syntax/common-table-expression.html">common-table-expression:</a></b>
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<button id='x1341' onclick='hideorshow("x1341","x1342")'>show</button></p>
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<div id='x1342' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram common-table-expression" src="images/syntax/common-table-expression.gif" />
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</div>
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<p><b><a href="syntax/compound-operator.html">compound-operator:</a></b>
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<button id='x1343' onclick='hideorshow("x1343","x1344")'>show</button></p>
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<div id='x1344' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram compound-operator" src="images/syntax/compound-operator.gif" />
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</div>
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<p><b><a href="syntax/join-clause.html">join-clause:</a></b>
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<button id='x1345' onclick='hideorshow("x1345","x1346")'>show</button></p>
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<div id='x1346' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram join-clause" src="images/syntax/join-clause.gif" />
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<p><b><a href="syntax/join-constraint.html">join-constraint:</a></b>
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<button id='x1347' onclick='hideorshow("x1347","x1348")'>show</button></p>
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<div id='x1348' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram join-constraint" src="images/syntax/join-constraint.gif" />
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</div>
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<p><b><a href="syntax/join-operator.html">join-operator:</a></b>
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<button id='x1349' onclick='hideorshow("x1349","x1350")'>show</button></p>
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<div id='x1350' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram join-operator" src="images/syntax/join-operator.gif" />
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</div>
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</div>
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<p><b><a href="syntax/ordering-term.html">ordering-term:</a></b>
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<button id='x1351' onclick='hideorshow("x1351","x1352")'>show</button></p>
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<div id='x1352' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram ordering-term" src="images/syntax/ordering-term.gif" />
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</div>
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<p><b><a href="syntax/result-column.html">result-column:</a></b>
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<button id='x1353' onclick='hideorshow("x1353","x1354")'>show</button></p>
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<div id='x1354' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram result-column" src="images/syntax/result-column.gif" />
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</div>
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<p><b><a href="syntax/table-or-subquery.html">table-or-subquery:</a></b>
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<button id='x1355' onclick='hideorshow("x1355","x1356")'>show</button></p>
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<div id='x1356' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram table-or-subquery" src="images/syntax/table-or-subquery.gif" />
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</div>
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<p><b><a href="syntax/window-defn.html">window-defn:</a></b>
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<button id='x1357' onclick='hideorshow("x1357","x1358")'>show</button></p>
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<div id='x1358' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram window-defn" src="images/syntax/window-defn.gif" />
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<p><b><a href="syntax/frame-spec.html">frame-spec:</a></b>
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<button id='x1359' onclick='hideorshow("x1359","x1360")'>show</button></p>
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<div id='x1360' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram frame-spec" src="images/syntax/frame-spec.gif" />
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</div>
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</div>
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</div>
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<p><b><a href="syntax/type-name.html">type-name:</a></b>
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<button id='x1361' onclick='hideorshow("x1361","x1362")'>show</button></p>
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<div id='x1362' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram type-name" src="images/syntax/type-name.gif" />
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<p><b><a href="syntax/signed-number.html">signed-number:</a></b>
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<button id='x1363' onclick='hideorshow("x1363","x1364")'>show</button></p>
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<div id='x1364' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram signed-number" src="images/syntax/signed-number.gif" />
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</div>
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</div>
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</div>
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<p><b><a href="syntax/indexed-column.html">indexed-column:</a></b>
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<button id='x1365' onclick='hideorshow("x1365","x1366")'>show</button></p>
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<div id='x1366' style='display:none;' class='imgcontainer'>
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<img alt="syntax diagram indexed-column" src="images/syntax/indexed-column.gif" />
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</div>
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</div>
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<p>The CREATE INDEX command consists of the keywords "CREATE INDEX" followed
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by the name of the new index, the keyword "ON", the name of a previously
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created table that is to be indexed, and a parenthesized list of table column
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names and/or expressions that are used for the index key.
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If the optional WHERE clause is included, then the index is a "<a href="partialindex.html">partial index</a>".
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</p>
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<p>If the optional IF NOT EXISTS clause is present and another index
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with the same name already exists, then this command becomes a no-op.</p>
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<p>There are no arbitrary limits on the number of indices that can be
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attached to a single table. The number of columns in an index is
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limited to the value set by
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<a href="c3ref/limit.html">sqlite3_limit</a>(<a href="c3ref/c_limit_attached.html#sqlitelimitcolumn">SQLITE_LIMIT_COLUMN</a>,...).</p>
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<p>Indexes are removed with the <a href="lang_dropindex.html">DROP INDEX</a> command.</p>
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<a name="uniqueidx"></a>
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<h2 id="unique_indexes"><span>1.1. </span>Unique Indexes</h2>
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<p>If the UNIQUE keyword appears between CREATE and INDEX then duplicate
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index entries are not allowed. Any attempt to insert a duplicate entry
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will result in an error.</p>
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<p>For the purposes of unique indices, all NULL values
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are considered different from all other NULL values and are thus unique.
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This is one of the two possible interpretations of the SQL-92 standard
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(the language in the standard is ambiguous). The interpretation used
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by SQLite is the same and is the interpretation
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followed by PostgreSQL, MySQL, Firebird, and Oracle. Informix and
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Microsoft SQL Server follow the other interpretation of the standard, which
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is that all NULL values are equal to one another.</p>
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<a name="indexexpr"></a>
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<h2 id="indexes_on_expressions"><span>1.2. </span>Indexes on Expressions</h2>
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<p>Expressions in an index may not reference other tables
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and may not use subqueries nor functions whose result might
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change (ex: <a href="lang_corefunc.html#random">random()</a> or <a href="lang_corefunc.html#sqlite_version">sqlite_version()</a>).
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Expressions in an index may only refer to columns in the table
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that is being indexed.
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Indexes on expression will not work with versions of SQLite prior
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to <a href="releaselog/3_9_0.html">version 3.9.0</a> (2015-10-14).
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See the <a href="expridx.html">Indexes On Expressions</a> document for additional information
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about using general expressions in CREATE INDEX statements.
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<a name="descidx"></a>
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</p><h2 id="descending_indexes"><span>1.3. </span>Descending Indexes</h2>
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<p>Each column name or expression can be followed by one
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of the "ASC" or "DESC" keywords to indicate sort order.
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The sort order may or may not be ignored depending
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on the database file format, and in particular the <a href="fileformat2.html#schemaformat">schema format number</a>.
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The "legacy" schema format (1) ignores index
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sort order. The descending index schema format (4) takes index sort order
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into account. Only versions of SQLite 3.3.0 (2006-01-11)
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and later are able to understand
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the descending index format. For compatibility, version of SQLite between 3.3.0
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and 3.7.9 use the legacy schema format by default. The newer schema format is
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used by default in version 3.7.10 (2012-01-16) and later.
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The <a href="pragma.html#pragma_legacy_file_format">legacy_file_format pragma</a> can be used to change set the specific
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behavior for any version of SQLite.</p>
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<h2 id="nulls_first_and_nulls_last"><span>1.4. </span>NULLS FIRST and NULLS LAST</h2>
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<p>The NULLS FIRST and NULLS LAST predicates are not supported
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for indexes. For <a href="datatype3.html#sortorder">sorting purposes</a>, SQLite considers NULL values
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to be smaller than all other values. Hence NULL values always appear at
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the beginning of an ASC index and at the end of a DESC index.</p>
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<a name="collidx"></a>
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<h2 id="collations"><span>1.5. </span>Collations</h2>
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<p>The COLLATE clause optionally following each column name
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or expression defines a
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collating sequence used for text entries in that column.
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The default collating
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sequence is the collating sequence defined for that column in the
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<a href="lang_createtable.html">CREATE TABLE</a> statement. Or if no collating sequence is otherwise defined,
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the built-in BINARY collating sequence is used.</p>
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