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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:17:33 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:17:33 +0000 |
| commit | 5e45211a64149b3c659b90ff2de6fa982a5a93ed (patch) | |
| tree | 739caf8c461053357daa9f162bef34516c7bf452 /doc/src/sgml/html/ddl-default.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.tar.xz postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.zip | |
Adding upstream version 15.5.upstream/15.5
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/ddl-default.html')
| -rw-r--r-- | doc/src/sgml/html/ddl-default.html | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/doc/src/sgml/html/ddl-default.html b/doc/src/sgml/html/ddl-default.html new file mode 100644 index 0000000..43c7883 --- /dev/null +++ b/doc/src/sgml/html/ddl-default.html @@ -0,0 +1,49 @@ +<?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>5.2. Default Values</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="ddl-basics.html" title="5.1. Table Basics" /><link rel="next" href="ddl-generated-columns.html" title="5.3. Generated Columns" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">5.2. Default Values</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ddl-basics.html" title="5.1. Table Basics">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ddl.html" title="Chapter 5. Data Definition">Up</a></td><th width="60%" align="center">Chapter 5. Data Definition</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="ddl-generated-columns.html" title="5.3. Generated Columns">Next</a></td></tr></table><hr /></div><div class="sect1" id="DDL-DEFAULT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">5.2. Default Values</h2></div></div></div><a id="id-1.5.4.4.2" class="indexterm"></a><p> + A column can be assigned a default value. When a new row is + created and no values are specified for some of the columns, those + columns will be filled with their respective default values. A + data manipulation command can also request explicitly that a column + be set to its default value, without having to know what that value is. + (Details about data manipulation commands are in <a class="xref" href="dml.html" title="Chapter 6. Data Manipulation">Chapter 6</a>.) + </p><p> + <a id="id-1.5.4.4.4.1" class="indexterm"></a> + If no default value is declared explicitly, the default value is the + null value. This usually makes sense because a null value can + be considered to represent unknown data. + </p><p> + In a table definition, default values are listed after the column + data type. For example: +</p><pre class="programlisting"> +CREATE TABLE products ( + product_no integer, + name text, + price numeric <span class="emphasis"><strong>DEFAULT 9.99</strong></span> +); +</pre><p> + </p><p> + The default value can be an expression, which will be + evaluated whenever the default value is inserted + (<span class="emphasis"><em>not</em></span> when the table is created). A common example + is for a <code class="type">timestamp</code> column to have a default of <code class="literal">CURRENT_TIMESTAMP</code>, + so that it gets set to the time of row insertion. Another common + example is generating a <span class="quote">“<span class="quote">serial number</span>”</span> for each row. + In <span class="productname">PostgreSQL</span> this is typically done by + something like: +</p><pre class="programlisting"> +CREATE TABLE products ( + product_no integer <span class="emphasis"><strong>DEFAULT nextval('products_product_no_seq')</strong></span>, + ... +); +</pre><p> + where the <code class="literal">nextval()</code> function supplies successive values + from a <em class="firstterm">sequence object</em> (see <a class="xref" href="functions-sequence.html" title="9.17. Sequence Manipulation Functions">Section 9.17</a>). This arrangement is sufficiently common + that there's a special shorthand for it: +</p><pre class="programlisting"> +CREATE TABLE products ( + product_no <span class="emphasis"><strong>SERIAL</strong></span>, + ... +); +</pre><p> + The <code class="literal">SERIAL</code> shorthand is discussed further in <a class="xref" href="datatype-numeric.html#DATATYPE-SERIAL" title="8.1.4. Serial Types">Section 8.1.4</a>. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ddl-basics.html" title="5.1. Table Basics">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ddl.html" title="Chapter 5. Data Definition">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ddl-generated-columns.html" title="5.3. Generated Columns">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5.1. Table Basics </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"> 5.3. Generated Columns</td></tr></table></div></body></html>
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