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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>6.2. Updating Data</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="dml-insert.html" title="6.1. Inserting Data" /><link rel="next" href="dml-delete.html" title="6.3. Deleting Data" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">6.2. Updating Data</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="dml-insert.html" title="6.1. Inserting Data">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="dml.html" title="Chapter 6. Data Manipulation">Up</a></td><th width="60%" align="center">Chapter 6. Data Manipulation</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="dml-delete.html" title="6.3. Deleting Data">Next</a></td></tr></table><hr /></div><div class="sect1" id="DML-UPDATE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">6.2. Updating Data</h2></div></div></div><a id="id-1.5.5.4.2" class="indexterm"></a><a id="id-1.5.5.4.3" class="indexterm"></a><p>
+   The modification of data that is already in the database is
+   referred to as updating.  You can update individual rows, all the
+   rows in a table, or a subset of all rows.  Each column can be
+   updated separately; the other columns are not affected.
+  </p><p>
+   To update existing rows, use the <a class="xref" href="sql-update.html" title="UPDATE"><span class="refentrytitle">UPDATE</span></a>
+   command.  This requires
+   three pieces of information:
+   </p><div class="orderedlist"><ol class="orderedlist compact" type="1"><li class="listitem"><p>The name of the table and column to update</p></li><li class="listitem"><p>The new value of the column</p></li><li class="listitem"><p>Which row(s) to update</p></li></ol></div><p>
+  </p><p>
+   Recall from <a class="xref" href="ddl.html" title="Chapter 5. Data Definition">Chapter 5</a> that SQL does not, in general,
+   provide a unique identifier for rows.  Therefore it is not
+   always possible to directly specify which row to update.
+   Instead, you specify which conditions a row must meet in order to
+   be updated.  Only if you have a primary key in the table (independent of
+   whether you declared it or not) can you reliably address individual rows
+   by choosing a condition that matches the primary key.
+   Graphical database access tools rely on this fact to allow you to
+   update rows individually.
+  </p><p>
+   For example, this command updates all products that have a price of
+   5 to have a price of 10:
+</p><pre class="programlisting">
+UPDATE products SET price = 10 WHERE price = 5;
+</pre><p>
+    This might cause zero, one, or many rows to be updated.  It is not
+    an error to attempt an update that does not match any rows.
+  </p><p>
+   Let's look at that command in detail. First is the key word
+   <code class="literal">UPDATE</code> followed by the table name.  As usual,
+   the table name can be schema-qualified, otherwise it is looked up
+   in the path.  Next is the key word <code class="literal">SET</code> followed
+   by the column name, an equal sign, and the new column value.  The
+   new column value can be any scalar expression, not just a constant.
+   For example, if you want to raise the price of all products by 10%
+   you could use:
+</p><pre class="programlisting">
+UPDATE products SET price = price * 1.10;
+</pre><p>
+   As you see, the expression for the new value can refer to the existing
+   value(s) in the row.  We also left out the <code class="literal">WHERE</code> clause.
+   If it is omitted, it means that all rows in the table are updated.
+   If it is present, only those rows that match the
+   <code class="literal">WHERE</code> condition are updated.  Note that the equals
+   sign in the <code class="literal">SET</code> clause is an assignment while
+   the one in the <code class="literal">WHERE</code> clause is a comparison, but
+   this does not create any ambiguity.  Of course, the
+   <code class="literal">WHERE</code> condition does
+   not have to be an equality test.  Many other operators are
+   available (see <a class="xref" href="functions.html" title="Chapter 9. Functions and Operators">Chapter 9</a>).  But the expression
+   needs to evaluate to a Boolean result.
+  </p><p>
+   You can update more than one column in an
+   <code class="command">UPDATE</code> command by listing more than one
+   assignment in the <code class="literal">SET</code> clause.  For example:
+</p><pre class="programlisting">
+UPDATE mytable SET a = 5, b = 3, c = 1 WHERE a &gt; 0;
+</pre><p>
+  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="dml-insert.html" title="6.1. Inserting Data">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="dml.html" title="Chapter 6. Data Manipulation">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="dml-delete.html" title="6.3. Deleting Data">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.1. Inserting Data </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 6.3. Deleting Data</td></tr></table></div></body></html>
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