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+<div class=fancy>
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+Generated Columns
+</div>
+<div class="fancy_toc">
+<a onclick="toggle_toc()">
+<span class="fancy_toc_mark" id="toc_mk">&#x25ba;</span>
+Table Of Contents
+</a>
+<div id="toc_sub"><div class="fancy-toc1"><a href="#introduction">1. Introduction</a></div>
+<div class="fancy-toc1"><a href="#syntax">2. Syntax</a></div>
+<div class="fancy-toc2"><a href="#virtual_versus_stored_columns">2.1. VIRTUAL versus STORED columns</a></div>
+<div class="fancy-toc2"><a href="#capabilities">2.2. Capabilities</a></div>
+<div class="fancy-toc2"><a href="#limitations">2.3. Limitations</a></div>
+<div class="fancy-toc1"><a href="#compatibility">3. Compatibility</a></div>
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+</div>
+
+
+
+
+<h1 id="introduction"><span>1. </span>Introduction</h1>
+
+<p>Generated columns (also sometimes called "computed columns")
+are columns of a table whose values are a function of other columns
+in the same row.
+Generated columns can be read, but their values can not be directly
+written. The only way to change the value of a generated column is to
+modify the values of the other columns used to calculate
+the generated column.
+
+</p><h1 id="syntax"><span>2. </span>Syntax</h1>
+
+<p>Syntactically, generated columns are designated using a
+"GENERATED ALWAYS" <a href="syntax/column-constraint.html">column-constraint</a>. For example:
+
+</p><div class="codeblock"><pre>CREATE TABLE t1(
+ a INTEGER PRIMARY KEY,
+ b INT,
+ c TEXT,
+ d INT GENERATED ALWAYS AS (a*abs(b)) VIRTUAL,
+ e TEXT GENERATED ALWAYS AS (substr(c,b,b+1)) STORED
+);
+</pre></div>
+
+<p>The statement above has three ordinary columns, "a" (the PRIMARY KEY),
+"b", and "c", and two generated columns "d" and "e".
+
+</p><p>The "GENERATED ALWAYS" keywords at the beginning of the constraint
+and the "VIRTUAL" or "STORED" keyword at the end are all optional.
+Only the "AS" keyword and the parenthesized expression are required.
+If the trailing "VIRTUAL" or "STORED" keyword is omitted, then
+VIRTUAL is the default. Hence, the example statement above could
+be simplified to just:
+
+</p><div class="codeblock"><pre>CREATE TABLE t1(
+ a INTEGER PRIMARY KEY,
+ b INT,
+ c TEXT,
+ d INT AS (a*abs(b)),
+ e TEXT AS (substr(c,b,b+1)) STORED
+);
+</pre></div>
+
+<h2 id="virtual_versus_stored_columns"><span>2.1. </span>VIRTUAL versus STORED columns</h2>
+
+<p>Generated columns can be either VIRTUAL or STORED. The value of
+a VIRTUAL column is computed when read, whereas the value of a STORED
+column is computed when the row is written. STORED columns take up space
+in the database file, whereas VIRTUAL columns use more CPU cycles when
+being read.
+
+</p><p>From the point of view of SQL, STORED and VIRTUAL columns are almost
+exactly the same. Queries against either class of generated column
+produce the same results. The only functional difference is that
+one cannot add new STORED columns using the
+<a href="lang_altertable.html#altertabaddcol">ALTER TABLE ADD COLUMN</a> command. Only VIRTUAL columns can be added
+using ALTER TABLE.
+
+</p><h2 id="capabilities"><span>2.2. </span>Capabilities</h2>
+
+<ol>
+<li><p>
+Generated columns can have a datatype. SQLite attempts to transform
+the result of the generating expression into that datatype using the
+same <a href="datatype3.html#affinity">affinity</a> rules as for ordinary columns.
+
+</p></li><li><p>
+Generated columns may have NOT NULL, CHECK, and UNIQUE constraints,
+and foreign key constraints, just like ordinary columns.
+
+</p></li><li><p>
+Generated columns can participate in indexes, just like ordinary
+columns.
+
+</p></li><li><p>
+The expression of a generated column can refer to any of the
+other declared columns in the table, including other generated columns,
+as long as the expression does not directly or indirectly refer back
+to itself.
+
+</p></li><li><p>
+Generated columns can occur anywhere in the table definition. Generated
+columns can be interspersed among ordinary columns. It is not necessary
+to put generated columns at the end of the list of columns in the
+table definition, as is shown in the examples above.
+</p></li></ol>
+
+
+<h2 id="limitations"><span>2.3. </span>Limitations</h2>
+
+<ol>
+<li><p>
+Generated columns may not have a <a href="lang_createtable.html#dfltval">default value</a> (they may not use the
+"DEFAULT" clause). The value of a generated column is always the value
+specified by the expression that follows the "AS" keyword.
+
+</p></li><li><p>
+Generated columns may not be used as part of the <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a>.
+(Future versions of SQLite might relax this constraint for STORED columns.)
+
+</p></li><li><p>
+The expression of a generated column may only reference
+constant literals and columns within the same row, and may only use
+scalar <a href="deterministic.html">deterministic functions</a>. The expression may not use subqueries,
+aggregate functions, window functions, or table-valued functions.
+
+</p></li><li><p>
+The expression of a generated column may refer to other generated columns
+in the same row, but no generated column can depend upon itself, either
+directly or indirectly.
+
+</p></li><li><p>The expression of a generated column may not directly reference
+the <a href="lang_createtable.html#rowid">ROWID</a>, though it can reference the <a href="lang_createtable.html#rowid">INTEGER PRIMARY KEY</a> column,
+which is often the same thing.
+
+</p></li><li><p>
+Every table must have at least one non-generated column.
+
+</p></li><li><p>
+It is not possible to <a href="lang_altertable.html#altertabaddcol">ALTER TABLE ADD COLUMN</a> a STORED column.
+One can add a VIRTUAL column, however.
+
+</p></li><li><p>
+The datatype and <a href="datatype3.html#collation">collating sequence</a> of the generated column are determined
+only by the datatype and <a href="lang_createtable.html#collateclause">COLLATE clause</a> on the column definition.
+The datatype and collating sequence of the GENERATED ALWAYS AS expression
+have no affect on the datatype and collating sequence of the column itself.
+
+</p></li><li><p>
+Generated columns are not included in the list of columns provided by
+the <a href="pragma.html#pragma_table_info">PRAGMA table_info</a> statement. But they are included in the output of
+the newer <a href="pragma.html#pragma_table_xinfo">PRAGMA table_xinfo</a> statement.
+</p></li></ol>
+
+<h1 id="compatibility"><span>3. </span>Compatibility</h1>
+
+<p>Generated column support was added with SQLite version 3.31.0
+(2020-01-22). If an earlier version of SQLite attempts to read
+a database file that contains a generated column in its schema, then
+that earlier version will perceive the generated column syntax as an
+error and will report that the database schema is corrupt.
+
+</p><p>To clarify: SQLite version 3.31.0 can read and write any database
+created by any prior version of SQLite going back to
+SQLite 3.0.0 (2004-06-18). And, earlier versions of SQLite,
+prior to 3.31.0, can read and write databases created by SQLite
+version 3.31.0 and later as long
+as the database schema does not contain features, such as
+generated columns, that are not understood by the earlier version.
+Problems only arise if you create a new database that contains
+generated columns, using SQLite version 3.31.0 or later, and then
+try to read or write that database file using an earlier version of
+SQLite that does not understand generated columns.
+</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/gencol.in?m=1b689d97b3fb3c295">2022-11-09 20:09:19</a> UTC </small></i></p>
+