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diff --git a/www/schematab.html b/www/schematab.html new file mode 100644 index 0000000..67cb180 --- /dev/null +++ b/www/schematab.html @@ -0,0 +1,281 @@ +<!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 Schema 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. 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Introduction</a></div> +<div class="fancy-toc1"><a href="#alternative_names">2. Alternative Names</a></div> +<div class="fancy-toc1"><a href="#interpretation_of_the_schema_table">3. Interpretation Of The Schema Table</a></div> +<div class="fancy-toc1"><a href="#creation_and_modification_of_the_schema_table">4. Creation and Modification Of The Schema Table</a></div> +</div> +</div> +<script> +function toggle_toc(){ +var sub = document.getElementById("toc_sub") +var mk = document.getElementById("toc_mk") +if( sub.style.display!="block" ){ +sub.style.display = "block"; +mk.innerHTML = "▼"; +} else { +sub.style.display = "none"; +mk.innerHTML = "►"; +} +} +</script> +</div> + + + + + +<h1 id="introduction"><span>1. </span>Introduction</h1> + +<p>Every SQLite database contains a single "schema table" that stores the +schema for that database. The schema for a database is a description of +all of the other tables, indexes, triggers, and views that are +contained within the database. The schema table looks like this: + +</p><blockquote><pre> +CREATE TABLE sqlite_schema( + type text, + name text, + tbl_name text, + rootpage integer, + sql text +); +</pre></blockquote> + +<p>The sqlite_schema table contains one row for each table, index, view, +and trigger (collectively "objects") in the schema, except there +is no entry for the sqlite_schema table itself. See the +<a href="fileformat2.html#ffschema">schema storage</a> subsection of the <a href="fileformat2.html">file format</a> documentation for +additional information on how SQLite uses the sqlite_schema table +internally. + +</p><h1 id="alternative_names"><span>2. </span>Alternative Names</h1> + +<p>The schema table can always be referenced using the name "sqlite_schema", +especially if qualifed by the schema name like +"main.sqlite_schema" or "temp.sqlite_schema". But for historical +compatibility, some alternative names are also recognized, including: + +</p><ol> +<li> sqlite_master +</li><li> sqlite_temp_schema +</li><li> sqlite_temp_master +</li></ol> + +<p> +Alternatives (2) and (3) only work for the TEMP database associated +with each database connection, but alternative (1) works anywhere. +For historical reasons, callbacks from the <a href="c3ref/set_authorizer.html">sqlite3_set_authorizer()</a> +interface always refer to the schema table using names (1) or (3). + +</p><h1 id="interpretation_of_the_schema_table"><span>3. </span>Interpretation Of The Schema Table</h1> + +<p>The meanings of the fields of the schema table are as follows: + +</p><dl> +<dt><b>type</b></dt> +<dd> +<p>The sqlite_schema.type column will be one +of the following text strings: 'table', 'index', 'view', or 'trigger' +according to the type of object defined. The 'table' string is used +for both ordinary and <a href="vtab.html">virtual tables</a>.</p> +</dd> + +<dt><b>name</b></dt><dt> +</dt><dd> +<p>The sqlite_schema.name column will hold the name of the object. +<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 +<a href="fileformat2.html#intschema">internal indexes</a> with names of the form "sqlite_autoindex_TABLE_N" +where TABLE is replaced by the name of the table that contains the +constraint and N is an integer beginning with 1 and increasing by one +with each constraint seen in the table definition. +In a <a href="withoutrowid.html">WITHOUT ROWID</a> table, there is no sqlite_schema entry for the +PRIMARY KEY, but the "sqlite_autoindex_TABLE_N" name is set aside +for the PRIMARY KEY as if the sqlite_schema entry did exist. This +will affect the numbering of subsequent UNIQUE constraints. +The "sqlite_autoindex_TABLE_N" name is never allocated for an +<a href="lang_createtable.html#rowid">INTEGER PRIMARY KEY</a>, either in rowid tables or WITHOUT ROWID tables. +</p> +</dd> + +<dt><b>tbl_name</b></dt> +<dd> +<p>The sqlite_schema.tbl_name column holds the name of a table or view +that the object is associated with. For a table or view, the +tbl_name column is a copy of the name column. For an index, the tbl_name +is the name of the table that is indexed. For a trigger, the tbl_name +column stores the name of the table or view that causes the trigger +to fire.</p> +</dd> + +<dt><b>rootpage</b></dt> +<dd> +<p>The sqlite_schema.rootpage column stores the page number of the root +b-tree page for tables and indexes. For rows that define views, triggers, +and virtual tables, the rootpage column is 0 or NULL.</p> +</dd> + +<dt><b>sql</b></dt> +<dd> +<p>The sqlite_schema.sql column stores SQL text that describes the +object. This SQL text is a <a href="lang_createtable.html">CREATE TABLE</a>, <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a>, +<a href="lang_createindex.html">CREATE INDEX</a>, +<a href="lang_createview.html">CREATE VIEW</a>, or <a href="lang_createtrigger.html">CREATE TRIGGER</a> statement that if evaluated against +the database file when it is the main database of a <a href="c3ref/sqlite3.html">database connection</a> +would recreate the object. The text is usually a copy of the original +statement used to create the object but with normalizations applied so +that the text conforms to the following rules: + +</p><ul> +<li>The CREATE, TABLE, VIEW, TRIGGER, and INDEX keywords at the beginning +of the statement are converted to all upper case letters. +</li><li>The TEMP or TEMPORARY keyword is removed if it occurs after the +initial CREATE keyword. +</li><li>Any database name qualifier that occurs prior to the name of the +object being created is removed. +</li><li>Leading spaces are removed. +</li><li>All spaces following the first two keywords are converted into a single +space. +</li></ul> + +<p>The text in the sqlite_schema.sql column is a copy of the original +CREATE statement text that created the object, except normalized as +described above and as modified by subsequent <a href="lang_altertable.html">ALTER TABLE</a> statements. +The sqlite_schema.sql is NULL for the <a href="fileformat2.html#intschema">internal indexes</a> that are +automatically created by <a href="lang_createtable.html#uniqueconst">UNIQUE</a> or <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> constraints.</p> +</dd> +</dl> + +<h1 id="creation_and_modification_of_the_schema_table"><span>4. </span>Creation and Modification Of The Schema Table</h1> + +<p>SQLite creates the schema table upon database creation and modifies +its content as SQLite users submit DDL statements for execution. There +is no need for users to modify it under normal circumstances, and they +bear the risk of <a href="howtocorrupt.html#cfgerr">database corruption</a> if they do modify it. +</p> + |