281 lines
10 KiB
HTML
281 lines
10 KiB
HTML
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<div class="fancy_title">
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The Schema Table
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<div class="fancy_toc">
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<span class="fancy_toc_mark" id="toc_mk">►</span>
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Table Of Contents
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</a>
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<div id="toc_sub"><div class="fancy-toc1"><a href="#introduction">1. Introduction</a></div>
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<div class="fancy-toc1"><a href="#alternative_names">2. Alternative Names</a></div>
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<div class="fancy-toc1"><a href="#interpretation_of_the_schema_table">3. Interpretation Of The Schema Table</a></div>
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<div class="fancy-toc1"><a href="#creation_and_modification_of_the_schema_table">4. Creation and Modification Of The Schema Table</a></div>
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<h1 id="introduction"><span>1. </span>Introduction</h1>
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<p>Every SQLite database contains a single "schema table" that stores the
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schema for that database. The schema for a database is a description of
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all of the other tables, indexes, triggers, and views that are
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contained within the database. The schema table looks like this:
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</p><blockquote><pre>
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CREATE TABLE sqlite_schema(
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type text,
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name text,
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tbl_name text,
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rootpage integer,
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sql text
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);
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</pre></blockquote>
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<p>The sqlite_schema table contains one row for each table, index, view,
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and trigger (collectively "objects") in the schema, except there
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is no entry for the sqlite_schema table itself. See the
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<a href="fileformat2.html#ffschema">schema storage</a> subsection of the <a href="fileformat2.html">file format</a> documentation for
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additional information on how SQLite uses the sqlite_schema table
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internally.
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</p><h1 id="alternative_names"><span>2. </span>Alternative Names</h1>
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<p>The schema table can always be referenced using the name "sqlite_schema",
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especially if qualifed by the schema name like
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"main.sqlite_schema" or "temp.sqlite_schema". But for historical
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compatibility, some alternative names are also recognized, including:
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</p><ol>
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<li> sqlite_master
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</li><li> sqlite_temp_schema
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</li><li> sqlite_temp_master
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</li></ol>
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<p>
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Alternatives (2) and (3) only work for the TEMP database associated
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with each database connection, but alternative (1) works anywhere.
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For historical reasons, callbacks from the <a href="c3ref/set_authorizer.html">sqlite3_set_authorizer()</a>
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interface always refer to the schema table using names (1) or (3).
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</p><h1 id="interpretation_of_the_schema_table"><span>3. </span>Interpretation Of The Schema Table</h1>
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<p>The meanings of the fields of the schema table are as follows:
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</p><dl>
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<dt><b>type</b></dt>
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<dd>
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<p>The sqlite_schema.type column will be one
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of the following text strings: 'table', 'index', 'view', or 'trigger'
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according to the type of object defined. The 'table' string is used
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for both ordinary and <a href="vtab.html">virtual tables</a>.</p>
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</dd>
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<dt><b>name</b></dt><dt>
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</dt><dd>
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<p>The sqlite_schema.name column will hold the name of the object.
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<a href="lang_createtable.html#uniqueconst">UNIQUE</a> and <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> constraints on tables cause SQLite to create
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<a href="fileformat2.html#intschema">internal indexes</a> with names of the form "sqlite_autoindex_TABLE_N"
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where TABLE is replaced by the name of the table that contains the
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constraint and N is an integer beginning with 1 and increasing by one
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with each constraint seen in the table definition.
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In a <a href="withoutrowid.html">WITHOUT ROWID</a> table, there is no sqlite_schema entry for the
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PRIMARY KEY, but the "sqlite_autoindex_TABLE_N" name is set aside
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for the PRIMARY KEY as if the sqlite_schema entry did exist. This
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will affect the numbering of subsequent UNIQUE constraints.
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The "sqlite_autoindex_TABLE_N" name is never allocated for an
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<a href="lang_createtable.html#rowid">INTEGER PRIMARY KEY</a>, either in rowid tables or WITHOUT ROWID tables.
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</p>
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</dd>
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<dt><b>tbl_name</b></dt>
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<dd>
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<p>The sqlite_schema.tbl_name column holds the name of a table or view
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that the object is associated with. For a table or view, the
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tbl_name column is a copy of the name column. For an index, the tbl_name
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is the name of the table that is indexed. For a trigger, the tbl_name
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column stores the name of the table or view that causes the trigger
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to fire.</p>
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</dd>
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<dt><b>rootpage</b></dt>
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<dd>
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<p>The sqlite_schema.rootpage column stores the page number of the root
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b-tree page for tables and indexes. For rows that define views, triggers,
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and virtual tables, the rootpage column is 0 or NULL.</p>
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</dd>
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<dt><b>sql</b></dt>
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<dd>
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<p>The sqlite_schema.sql column stores SQL text that describes the
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object. This SQL text is a <a href="lang_createtable.html">CREATE TABLE</a>, <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a>,
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<a href="lang_createindex.html">CREATE INDEX</a>,
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<a href="lang_createview.html">CREATE VIEW</a>, or <a href="lang_createtrigger.html">CREATE TRIGGER</a> statement that if evaluated against
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the database file when it is the main database of a <a href="c3ref/sqlite3.html">database connection</a>
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would recreate the object. The text is usually a copy of the original
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statement used to create the object but with normalizations applied so
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that the text conforms to the following rules:
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</p><ul>
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<li>The CREATE, TABLE, VIEW, TRIGGER, and INDEX keywords at the beginning
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of the statement are converted to all upper case letters.
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</li><li>The TEMP or TEMPORARY keyword is removed if it occurs after the
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initial CREATE keyword.
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</li><li>Any database name qualifier that occurs prior to the name of the
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object being created is removed.
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</li><li>Leading spaces are removed.
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</li><li>All spaces following the first two keywords are converted into a single
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space.
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</li></ul>
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<p>The text in the sqlite_schema.sql column is a copy of the original
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CREATE statement text that created the object, except normalized as
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described above and as modified by subsequent <a href="lang_altertable.html">ALTER TABLE</a> statements.
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The sqlite_schema.sql is NULL for the <a href="fileformat2.html#intschema">internal indexes</a> that are
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automatically created by <a href="lang_createtable.html#uniqueconst">UNIQUE</a> or <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> constraints.</p>
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</dd>
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</dl>
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<h1 id="creation_and_modification_of_the_schema_table"><span>4. </span>Creation and Modification Of The Schema Table</h1>
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<p>SQLite creates the schema table upon database creation and modifies
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its content as SQLite users submit DDL statements for execution. There
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is no need for users to modify it under normal circumstances, and they
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bear the risk of <a href="howtocorrupt.html#cfgerr">database corruption</a> if they do modify it.
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</p>
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