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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>8.3. Character Types</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="datatype-money.html" title="8.2. Monetary Types" /><link rel="next" href="datatype-binary.html" title="8.4. Binary Data Types" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">8.3. Character Types</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="datatype-money.html" title="8.2. Monetary Types">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="datatype.html" title="Chapter 8. Data Types">Up</a></td><th width="60%" align="center">Chapter 8. Data Types</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="datatype-binary.html" title="8.4. Binary Data Types">Next</a></td></tr></table><hr /></div><div class="sect1" id="DATATYPE-CHARACTER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">8.3. Character Types <a href="#DATATYPE-CHARACTER" class="id_link">#</a></h2></div></div></div><a id="id-1.5.7.11.2" class="indexterm"></a><a id="id-1.5.7.11.3" class="indexterm"></a><a id="id-1.5.7.11.4" class="indexterm"></a><a id="id-1.5.7.11.5" class="indexterm"></a><a id="id-1.5.7.11.6" class="indexterm"></a><a id="id-1.5.7.11.7" class="indexterm"></a><a id="id-1.5.7.11.8" class="indexterm"></a><a id="id-1.5.7.11.9" class="indexterm"></a><div class="table" id="DATATYPE-CHARACTER-TABLE"><p class="title"><strong>Table 8.4. Character Types</strong></p><div class="table-contents"><table class="table" summary="Character Types" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>Name</th><th>Description</th></tr></thead><tbody><tr><td><code class="type">character varying(<em class="replaceable"><code>n</code></em>)</code>, <code class="type">varchar(<em class="replaceable"><code>n</code></em>)</code></td><td>variable-length with limit</td></tr><tr><td><code class="type">character(<em class="replaceable"><code>n</code></em>)</code>, <code class="type">char(<em class="replaceable"><code>n</code></em>)</code>, <code class="type">bpchar(<em class="replaceable"><code>n</code></em>)</code></td><td>fixed-length, blank-padded</td></tr><tr><td><code class="type">bpchar</code></td><td>variable unlimited length, blank-trimmed</td></tr><tr><td><code class="type">text</code></td><td>variable unlimited length</td></tr></tbody></table></div></div><br class="table-break" /><p>
<a class="xref" href="datatype-character.html#DATATYPE-CHARACTER-TABLE" title="Table 8.4. Character Types">Table 8.4</a> shows the
general-purpose character types available in
<span class="productname">PostgreSQL</span>.
</p><p>
<acronym class="acronym">SQL</acronym> defines two primary character types:
<code class="type">character varying(<em class="replaceable"><code>n</code></em>)</code> and
<code class="type">character(<em class="replaceable"><code>n</code></em>)</code>, where <em class="replaceable"><code>n</code></em>
is a positive integer. Both of these types can store strings up to
<em class="replaceable"><code>n</code></em> characters (not bytes) in length. An attempt to store a
longer string into a column of these types will result in an
error, unless the excess characters are all spaces, in which case
the string will be truncated to the maximum length. (This somewhat
bizarre exception is required by the <acronym class="acronym">SQL</acronym>
standard.)
However, if one explicitly casts a value to <code class="type">character
varying(<em class="replaceable"><code>n</code></em>)</code> or
<code class="type">character(<em class="replaceable"><code>n</code></em>)</code>, then an over-length
value will be truncated to <em class="replaceable"><code>n</code></em> characters without
raising an error. (This too is required by the
<acronym class="acronym">SQL</acronym> standard.)
If the string to be stored is shorter than the declared
length, values of type <code class="type">character</code> will be space-padded;
values of type <code class="type">character varying</code> will simply store the
shorter
string.
</p><p>
In addition, <span class="productname">PostgreSQL</span> provides the
<code class="type">text</code> type, which stores strings of any length.
Although the <code class="type">text</code> type is not in the
<acronym class="acronym">SQL</acronym> standard, several other SQL database
management systems have it as well.
<code class="type">text</code> is <span class="productname">PostgreSQL</span>'s native
string data type, in that most built-in functions operating on strings
are declared to take or return <code class="type">text</code> not <code class="type">character
varying</code>. For many purposes, <code class="type">character varying</code>
acts as though it were a <a class="link" href="domains.html" title="8.18. Domain Types">domain</a>
over <code class="type">text</code>.
</p><p>
The type name <code class="type">varchar</code> is an alias for <code class="type">character
varying</code>, while <code class="type">bpchar</code> (with length specifier) and
<code class="type">char</code> are aliases for <code class="type">character</code>. The
<code class="type">varchar</code> and <code class="type">char</code> aliases are defined in the
<acronym class="acronym">SQL</acronym> standard; <code class="type">bpchar</code> is a
<span class="productname">PostgreSQL</span> extension.
</p><p>
If specified, the length <em class="replaceable"><code>n</code></em> must be greater
than zero and cannot exceed 10,485,760. If <code class="type">character
varying</code> (or <code class="type">varchar</code>) is used without
length specifier, the type accepts strings of any length. If
<code class="type">bpchar</code> lacks a length specifier, it also accepts strings
of any length, but trailing spaces are semantically insignificant.
If <code class="type">character</code> (or <code class="type">char</code>) lacks a specifier,
it is equivalent to <code class="type">character(1)</code>.
</p><p>
Values of type <code class="type">character</code> are physically padded
with spaces to the specified width <em class="replaceable"><code>n</code></em>, and are
stored and displayed that way. However, trailing spaces are treated as
semantically insignificant and disregarded when comparing two values
of type <code class="type">character</code>. In collations where whitespace
is significant, this behavior can produce unexpected results;
for example <code class="command">SELECT 'a '::CHAR(2) collate "C" <
E'a\n'::CHAR(2)</code> returns true, even though <code class="literal">C</code>
locale would consider a space to be greater than a newline.
Trailing spaces are removed when converting a <code class="type">character</code> value
to one of the other string types. Note that trailing spaces
<span class="emphasis"><em>are</em></span> semantically significant in
<code class="type">character varying</code> and <code class="type">text</code> values, and
when using pattern matching, that is <code class="literal">LIKE</code> and
regular expressions.
</p><p>
The characters that can be stored in any of these data types are
determined by the database character set, which is selected when
the database is created. Regardless of the specific character set,
the character with code zero (sometimes called NUL) cannot be stored.
For more information refer to <a class="xref" href="multibyte.html" title="24.3. Character Set Support">Section 24.3</a>.
</p><p>
The storage requirement for a short string (up to 126 bytes) is 1 byte
plus the actual string, which includes the space padding in the case of
<code class="type">character</code>. Longer strings have 4 bytes of overhead instead
of 1. Long strings are compressed by the system automatically, so
the physical requirement on disk might be less. Very long values are also
stored in background tables so that they do not interfere with rapid
access to shorter column values. In any case, the longest
possible character string that can be stored is about 1 GB. (The
maximum value that will be allowed for <em class="replaceable"><code>n</code></em> in the data
type declaration is less than that. It wouldn't be useful to
change this because with multibyte character encodings the number of
characters and bytes can be quite different. If you desire to
store long strings with no specific upper limit, use
<code class="type">text</code> or <code class="type">character varying</code> without a length
specifier, rather than making up an arbitrary length limit.)
</p><div class="tip"><h3 class="title">Tip</h3><p>
There is no performance difference among these three types,
apart from increased storage space when using the blank-padded
type, and a few extra CPU cycles to check the length when storing into
a length-constrained column. While
<code class="type">character(<em class="replaceable"><code>n</code></em>)</code> has performance
advantages in some other database systems, there is no such advantage in
<span class="productname">PostgreSQL</span>; in fact
<code class="type">character(<em class="replaceable"><code>n</code></em>)</code> is usually the slowest of
the three because of its additional storage costs. In most situations
<code class="type">text</code> or <code class="type">character varying</code> should be used
instead.
</p></div><p>
Refer to <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" title="4.1.2.1. String Constants">Section 4.1.2.1</a> for information about
the syntax of string literals, and to <a class="xref" href="functions.html" title="Chapter 9. Functions and Operators">Chapter 9</a>
for information about available operators and functions.
</p><div class="example" id="id-1.5.7.11.21"><p class="title"><strong>Example 8.1. Using the Character Types</strong></p><div class="example-contents"><pre class="programlisting">
CREATE TABLE test1 (a character(4));
INSERT INTO test1 VALUES ('ok');
SELECT a, char_length(a) FROM test1; -- <span id="co.datatype-char"></span>(1)
<code class="computeroutput">
a | char_length
------+-------------
ok | 2
</code>
CREATE TABLE test2 (b varchar(5));
INSERT INTO test2 VALUES ('ok');
INSERT INTO test2 VALUES ('good ');
INSERT INTO test2 VALUES ('too long');
<code class="computeroutput">ERROR: value too long for type character varying(5)</code>
INSERT INTO test2 VALUES ('too long'::varchar(5)); -- explicit truncation
SELECT b, char_length(b) FROM test2;
<code class="computeroutput">
b | char_length
-------+-------------
ok | 2
good | 5
too l | 5
</code>
</pre><div class="calloutlist"><table border="0" summary="Callout list"><tr><td width="5%" valign="top" align="left"><p><a href="#co.datatype-char">(1)</a> </p></td><td valign="top" align="left"><p>
The <code class="function">char_length</code> function is discussed in
<a class="xref" href="functions-string.html" title="9.4. String Functions and Operators">Section 9.4</a>.
</p></td></tr></table></div></div></div><br class="example-break" /><p>
There are two other fixed-length character types in
<span class="productname">PostgreSQL</span>, shown in <a class="xref" href="datatype-character.html#DATATYPE-CHARACTER-SPECIAL-TABLE" title="Table 8.5. Special Character Types">Table 8.5</a>.
These are not intended for general-purpose use, only for use
in the internal system catalogs.
The <code class="type">name</code> type is used to store identifiers. Its
length is currently defined as 64 bytes (63 usable characters plus
terminator) but should be referenced using the constant
<code class="symbol">NAMEDATALEN</code> in <code class="literal">C</code> source code.
The length is set at compile time (and
is therefore adjustable for special uses); the default maximum
length might change in a future release. The type <code class="type">"char"</code>
(note the quotes) is different from <code class="type">char(1)</code> in that it
only uses one byte of storage, and therefore can store only a single
ASCII character. It is used in the system
catalogs as a simplistic enumeration type.
</p><div class="table" id="DATATYPE-CHARACTER-SPECIAL-TABLE"><p class="title"><strong>Table 8.5. Special Character Types</strong></p><div class="table-contents"><table class="table" summary="Special Character Types" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Storage Size</th><th>Description</th></tr></thead><tbody><tr><td><code class="type">"char"</code></td><td>1 byte</td><td>single-byte internal type</td></tr><tr><td><code class="type">name</code></td><td>64 bytes</td><td>internal type for object names</td></tr></tbody></table></div></div><br class="table-break" /></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="datatype-money.html" title="8.2. Monetary Types">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="datatype.html" title="Chapter 8. Data Types">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="datatype-binary.html" title="8.4. Binary Data Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">8.2. Monetary Types </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 8.4. Binary Data Types</td></tr></table></div></body></html>