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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:19:15 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:19:15 +0000 |
| commit | 6eb9c5a5657d1fe77b55cc261450f3538d35a94d (patch) | |
| tree | 657d8194422a5daccecfd42d654b8a245ef7b4c8 /doc/src/sgml/html/dml-update.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-13-upstream.tar.xz postgresql-13-upstream.zip | |
Adding upstream version 13.4.upstream/13.4upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/dml-update.html')
| -rw-r--r-- | doc/src/sgml/html/dml-update.html | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/doc/src/sgml/html/dml-update.html b/doc/src/sgml/html/dml-update.html new file mode 100644 index 0000000..7c56bd0 --- /dev/null +++ b/doc/src/sgml/html/dml-update.html @@ -0,0 +1,61 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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 V1.79.1" /><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 xmlns="http://www.w3.org/TR/xhtml1/transitional" 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 13.4 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></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 > 0; +</pre><p> + </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></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 13.4 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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