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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>CREATE TYPE</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="sql-createtrigger.html" title="CREATE TRIGGER" /><link rel="next" href="sql-createuser.html" title="CREATE USER" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE TYPE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createtrigger.html" title="CREATE TRIGGER">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-createuser.html" title="CREATE USER">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="SQL-CREATETYPE"><div class="titlepage"></div><a id="id-1.9.3.94.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE TYPE</span></h2><p>CREATE TYPE — define a new data type</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
CREATE TYPE <em class="replaceable"><code>name</code></em> AS
( [ <em class="replaceable"><code>attribute_name</code></em> <em class="replaceable"><code>data_type</code></em> [ COLLATE <em class="replaceable"><code>collation</code></em> ] [, ... ] ] )
CREATE TYPE <em class="replaceable"><code>name</code></em> AS ENUM
( [ '<em class="replaceable"><code>label</code></em>' [, ... ] ] )
CREATE TYPE <em class="replaceable"><code>name</code></em> AS RANGE (
SUBTYPE = <em class="replaceable"><code>subtype</code></em>
[ , SUBTYPE_OPCLASS = <em class="replaceable"><code>subtype_operator_class</code></em> ]
[ , COLLATION = <em class="replaceable"><code>collation</code></em> ]
[ , CANONICAL = <em class="replaceable"><code>canonical_function</code></em> ]
[ , SUBTYPE_DIFF = <em class="replaceable"><code>subtype_diff_function</code></em> ]
)
CREATE TYPE <em class="replaceable"><code>name</code></em> (
INPUT = <em class="replaceable"><code>input_function</code></em>,
OUTPUT = <em class="replaceable"><code>output_function</code></em>
[ , RECEIVE = <em class="replaceable"><code>receive_function</code></em> ]
[ , SEND = <em class="replaceable"><code>send_function</code></em> ]
[ , TYPMOD_IN = <em class="replaceable"><code>type_modifier_input_function</code></em> ]
[ , TYPMOD_OUT = <em class="replaceable"><code>type_modifier_output_function</code></em> ]
[ , ANALYZE = <em class="replaceable"><code>analyze_function</code></em> ]
[ , INTERNALLENGTH = { <em class="replaceable"><code>internallength</code></em> | VARIABLE } ]
[ , PASSEDBYVALUE ]
[ , ALIGNMENT = <em class="replaceable"><code>alignment</code></em> ]
[ , STORAGE = <em class="replaceable"><code>storage</code></em> ]
[ , LIKE = <em class="replaceable"><code>like_type</code></em> ]
[ , CATEGORY = <em class="replaceable"><code>category</code></em> ]
[ , PREFERRED = <em class="replaceable"><code>preferred</code></em> ]
[ , DEFAULT = <em class="replaceable"><code>default</code></em> ]
[ , ELEMENT = <em class="replaceable"><code>element</code></em> ]
[ , DELIMITER = <em class="replaceable"><code>delimiter</code></em> ]
[ , COLLATABLE = <em class="replaceable"><code>collatable</code></em> ]
)
CREATE TYPE <em class="replaceable"><code>name</code></em>
</pre></div><div class="refsect1" id="id-1.9.3.94.5"><h2>Description</h2><p>
<code class="command">CREATE TYPE</code> registers a new data type for use in
the current database. The user who defines a type becomes its
owner.
</p><p>
If a schema name is given then the type is created in the specified
schema. Otherwise it is created in the current schema. The type
name must be distinct from the name of any existing type or domain
in the same schema. (Because tables have associated data types,
the type name must also be distinct from the name of any existing
table in the same schema.)
</p><p>
There are five forms of <code class="command">CREATE TYPE</code>, as shown in the
syntax synopsis above. They respectively create a <em class="firstterm">composite
type</em>, an <em class="firstterm">enum type</em>, a <em class="firstterm">range type</em>, a
<em class="firstterm">base type</em>, or a <em class="firstterm">shell type</em>. The first four
of these are discussed in turn below. A shell type is simply a placeholder
for a type to be defined later; it is created by issuing <code class="command">CREATE
TYPE</code> with no parameters except for the type name. Shell types
are needed as forward references when creating range types and base types,
as discussed in those sections.
</p><div class="refsect2" id="id-1.9.3.94.5.5"><h3>Composite Types</h3><p>
The first form of <code class="command">CREATE TYPE</code>
creates a composite type.
The composite type is specified by a list of attribute names and data types.
An attribute's collation can be specified too, if its data type is
collatable. A composite type is essentially the same as the row type
of a table, but using <code class="command">CREATE TYPE</code> avoids the need to
create an actual table when all that is wanted is to define a type.
A stand-alone composite type is useful, for example, as the argument or
return type of a function.
</p><p>
To be able to create a composite type, you must
have <code class="literal">USAGE</code> privilege on all attribute types.
</p></div><div class="refsect2" id="SQL-CREATETYPE-ENUM"><h3>Enumerated Types</h3><p>
The second form of <code class="command">CREATE TYPE</code> creates an enumerated
(enum) type, as described in <a class="xref" href="datatype-enum.html" title="8.7. Enumerated Types">Section 8.7</a>.
Enum types take a list of quoted labels, each of which
must be less than <code class="symbol">NAMEDATALEN</code> bytes long (64 bytes in a
standard <span class="productname">PostgreSQL</span> build). (It is possible to
create an enumerated type with zero labels, but such a type cannot be used
to hold values before at least one label is added using <a class="xref" href="sql-altertype.html" title="ALTER TYPE"><span class="refentrytitle">ALTER TYPE</span></a>.)
</p></div><div class="refsect2" id="SQL-CREATETYPE-RANGE"><h3>Range Types</h3><p>
The third form of <code class="command">CREATE TYPE</code> creates a new
range type, as described in <a class="xref" href="rangetypes.html" title="8.17. Range Types">Section 8.17</a>.
</p><p>
The range type's <em class="replaceable"><code>subtype</code></em> can
be any type with an associated b-tree operator class (to determine the
ordering of values for the range type). Normally the subtype's default
b-tree operator class is used to determine ordering; to use a non-default
operator class, specify its name with <em class="replaceable"><code>subtype_opclass</code></em>. If the subtype is
collatable, and you want to use a non-default collation in the range's
ordering, specify the desired collation with the <em class="replaceable"><code>collation</code></em> option.
</p><p>
The optional <em class="replaceable"><code>canonical</code></em>
function must take one argument of the range type being defined, and
return a value of the same type. This is used to convert range values
to a canonical form, when applicable. See <a class="xref" href="rangetypes.html#RANGETYPES-DEFINING" title="8.17.8. Defining New Range Types">Section 8.17.8</a> for more information. Creating a
<em class="replaceable"><code>canonical</code></em> function
is a bit tricky, since it must be defined before the range type can be
declared. To do this, you must first create a shell type, which is a
placeholder type that has no properties except a name and an
owner. This is done by issuing the command <code class="literal">CREATE TYPE
<em class="replaceable"><code>name</code></em></code>, with no additional parameters. Then
the function can be declared using the shell type as argument and result,
and finally the range type can be declared using the same name. This
automatically replaces the shell type entry with a valid range type.
</p><p>
The optional <em class="replaceable"><code>subtype_diff</code></em>
function must take two values of the
<em class="replaceable"><code>subtype</code></em> type as argument,
and return a <code class="type">double precision</code> value representing the
difference between the two given values. While this is optional,
providing it allows much greater efficiency of GiST indexes on columns of
the range type. See <a class="xref" href="rangetypes.html#RANGETYPES-DEFINING" title="8.17.8. Defining New Range Types">Section 8.17.8</a> for more
information.
</p></div><div class="refsect2" id="id-1.9.3.94.5.8"><h3>Base Types</h3><p>
The fourth form of <code class="command">CREATE TYPE</code> creates a new base type
(scalar type). To create a new base type, you must be a superuser.
(This restriction is made because an erroneous type definition could
confuse or even crash the server.)
</p><p>
The parameters can appear in any order, not only that
illustrated above, and most are optional. You must register
two or more functions (using <code class="command">CREATE FUNCTION</code>) before
defining the type. The support functions
<em class="replaceable"><code>input_function</code></em> and
<em class="replaceable"><code>output_function</code></em>
are required, while the functions
<em class="replaceable"><code>receive_function</code></em>,
<em class="replaceable"><code>send_function</code></em>,
<em class="replaceable"><code>type_modifier_input_function</code></em>,
<em class="replaceable"><code>type_modifier_output_function</code></em> and
<em class="replaceable"><code>analyze_function</code></em>
are optional. Generally these functions have to be coded in C
or another low-level language.
</p><p>
The <em class="replaceable"><code>input_function</code></em>
converts the type's external textual representation to the internal
representation used by the operators and functions defined for the type.
<em class="replaceable"><code>output_function</code></em>
performs the reverse transformation. The input function can be
declared as taking one argument of type <code class="type">cstring</code>,
or as taking three arguments of types
<code class="type">cstring</code>, <code class="type">oid</code>, <code class="type">integer</code>.
The first argument is the input text as a C string, the second
argument is the type's own OID (except for array types, which instead
receive their element type's OID),
and the third is the <code class="literal">typmod</code> of the destination column, if known
(-1 will be passed if not).
The input function must return a value of the data type itself.
Usually, an input function should be declared STRICT; if it is not,
it will be called with a NULL first parameter when reading a NULL
input value. The function must still return NULL in this case, unless
it raises an error.
(This case is mainly meant to support domain input functions, which
might need to reject NULL inputs.)
The output function must be
declared as taking one argument of the new data type.
The output function must return type <code class="type">cstring</code>.
Output functions are not invoked for NULL values.
</p><p>
The optional <em class="replaceable"><code>receive_function</code></em>
converts the type's external binary representation to the internal
representation. If this function is not supplied, the type cannot
participate in binary input. The binary representation should be
chosen to be cheap to convert to internal form, while being reasonably
portable. (For example, the standard integer data types use network
byte order as the external binary representation, while the internal
representation is in the machine's native byte order.) The receive
function should perform adequate checking to ensure that the value is
valid.
The receive function can be declared as taking one argument of type
<code class="type">internal</code>, or as taking three arguments of types
<code class="type">internal</code>, <code class="type">oid</code>, <code class="type">integer</code>.
The first argument is a pointer to a <code class="type">StringInfo</code> buffer
holding the received byte string; the optional arguments are the
same as for the text input function.
The receive function must return a value of the data type itself.
Usually, a receive function should be declared STRICT; if it is not,
it will be called with a NULL first parameter when reading a NULL
input value. The function must still return NULL in this case, unless
it raises an error.
(This case is mainly meant to support domain receive functions, which
might need to reject NULL inputs.)
Similarly, the optional
<em class="replaceable"><code>send_function</code></em> converts
from the internal representation to the external binary representation.
If this function is not supplied, the type cannot participate in binary
output. The send function must be
declared as taking one argument of the new data type.
The send function must return type <code class="type">bytea</code>.
Send functions are not invoked for NULL values.
</p><p>
You should at this point be wondering how the input and output functions
can be declared to have results or arguments of the new type, when they
have to be created before the new type can be created. The answer is that
the type should first be defined as a <em class="firstterm">shell type</em>, which is a
placeholder type that has no properties except a name and an owner. This
is done by issuing the command <code class="literal">CREATE TYPE
<em class="replaceable"><code>name</code></em></code>, with no additional parameters. Then the
C I/O functions can be defined referencing the shell type. Finally,
<code class="command">CREATE TYPE</code> with a full definition replaces the shell entry
with a complete, valid type definition, after which the new type can be
used normally.
</p><p>
The optional
<em class="replaceable"><code>type_modifier_input_function</code></em>
and <em class="replaceable"><code>type_modifier_output_function</code></em>
are needed if the type supports modifiers, that is optional constraints
attached to a type declaration, such as <code class="literal">char(5)</code> or
<code class="literal">numeric(30,2)</code>. <span class="productname">PostgreSQL</span> allows
user-defined types to take one or more simple constants or identifiers as
modifiers. However, this information must be capable of being packed into a
single non-negative integer value for storage in the system catalogs. The
<em class="replaceable"><code>type_modifier_input_function</code></em>
is passed the declared modifier(s) in the form of a <code class="type">cstring</code>
array. It must check the values for validity (throwing an error if they
are wrong), and if they are correct, return a single non-negative
<code class="type">integer</code> value that will be stored as the column <span class="quote">“<span class="quote">typmod</span>”</span>.
Type modifiers will be rejected if the type does not have a
<em class="replaceable"><code>type_modifier_input_function</code></em>.
The <em class="replaceable"><code>type_modifier_output_function</code></em>
converts the internal integer typmod value back to the correct form for
user display. It must return a <code class="type">cstring</code> value that is the exact
string to append to the type name; for example <code class="type">numeric</code>'s
function might return <code class="literal">(30,2)</code>.
It is allowed to omit the
<em class="replaceable"><code>type_modifier_output_function</code></em>,
in which case the default display format is just the stored typmod integer
value enclosed in parentheses.
</p><p>
The optional <em class="replaceable"><code>analyze_function</code></em>
performs type-specific statistics collection for columns of the data type.
By default, <code class="command">ANALYZE</code> will attempt to gather statistics using
the type's <span class="quote">“<span class="quote">equals</span>”</span> and <span class="quote">“<span class="quote">less-than</span>”</span> operators, if there
is a default b-tree operator class for the type. For non-scalar types
this behavior is likely to be unsuitable, so it can be overridden by
specifying a custom analysis function. The analysis function must be
declared to take a single argument of type <code class="type">internal</code>, and return
a <code class="type">boolean</code> result. The detailed API for analysis functions appears
in <code class="filename">src/include/commands/vacuum.h</code>.
</p><p>
While the details of the new type's internal representation are only
known to the I/O functions and other functions you create to work with
the type, there are several properties of the internal representation
that must be declared to <span class="productname">PostgreSQL</span>.
Foremost of these is
<em class="replaceable"><code>internallength</code></em>.
Base data types can be fixed-length, in which case
<em class="replaceable"><code>internallength</code></em> is a
positive integer, or variable-length, indicated by setting
<em class="replaceable"><code>internallength</code></em>
to <code class="literal">VARIABLE</code>. (Internally, this is represented
by setting <code class="literal">typlen</code> to -1.) The internal representation of all
variable-length types must start with a 4-byte integer giving the total
length of this value of the type. (Note that the length field is often
encoded, as described in <a class="xref" href="storage-toast.html" title="68.2. TOAST">Section 68.2</a>; it's unwise
to access it directly.)
</p><p>
The optional flag <code class="literal">PASSEDBYVALUE</code> indicates that
values of this data type are passed by value, rather than by
reference. Types passed by value must be fixed-length, and their internal
representation cannot be larger than the size of the <code class="type">Datum</code> type
(4 bytes on some machines, 8 bytes on others).
</p><p>
The <em class="replaceable"><code>alignment</code></em> parameter
specifies the storage alignment required for the data type. The
allowed values equate to alignment on 1, 2, 4, or 8 byte boundaries.
Note that variable-length types must have an alignment of at least
4, since they necessarily contain an <code class="type">int4</code> as their first component.
</p><p>
The <em class="replaceable"><code>storage</code></em> parameter
allows selection of storage strategies for variable-length data
types. (Only <code class="literal">plain</code> is allowed for fixed-length
types.) <code class="literal">plain</code> specifies that data of the type
will always be stored in-line and not compressed.
<code class="literal">extended</code> specifies that the system will first
try to compress a long data value, and will move the value out of
the main table row if it's still too long.
<code class="literal">external</code> allows the value to be moved out of the
main table, but the system will not try to compress it.
<code class="literal">main</code> allows compression, but discourages moving
the value out of the main table. (Data items with this storage
strategy might still be moved out of the main table if there is no
other way to make a row fit, but they will be kept in the main
table preferentially over <code class="literal">extended</code> and
<code class="literal">external</code> items.)
</p><p>
All <em class="replaceable"><code>storage</code></em> values other
than <code class="literal">plain</code> imply that the functions of the data type
can handle values that have been <em class="firstterm">toasted</em>, as described
in <a class="xref" href="storage-toast.html" title="68.2. TOAST">Section 68.2</a> and <a class="xref" href="xtypes.html#XTYPES-TOAST" title="38.12.1. TOAST Considerations">Section 38.12.1</a>.
The specific other value given merely determines the default TOAST
storage strategy for columns of a toastable data type; users can pick
other strategies for individual columns using <code class="literal">ALTER TABLE
SET STORAGE</code>.
</p><p>
The <em class="replaceable"><code>like_type</code></em> parameter
provides an alternative method for specifying the basic representation
properties of a data type: copy them from some existing type. The values of
<em class="replaceable"><code>internallength</code></em>,
<em class="replaceable"><code>passedbyvalue</code></em>,
<em class="replaceable"><code>alignment</code></em>, and
<em class="replaceable"><code>storage</code></em> are copied from the
named type. (It is possible, though usually undesirable, to override
some of these values by specifying them along with the <code class="literal">LIKE</code>
clause.) Specifying representation this way is especially useful when
the low-level implementation of the new type <span class="quote">“<span class="quote">piggybacks</span>”</span> on an
existing type in some fashion.
</p><p>
The <em class="replaceable"><code>category</code></em> and
<em class="replaceable"><code>preferred</code></em> parameters can be
used to help control which implicit cast will be applied in ambiguous
situations. Each data type belongs to a category named by a single ASCII
character, and each type is either <span class="quote">“<span class="quote">preferred</span>”</span> or not within its
category. The parser will prefer casting to preferred types (but only from
other types within the same category) when this rule is helpful in
resolving overloaded functions or operators. For more details see <a class="xref" href="typeconv.html" title="Chapter 10. Type Conversion">Chapter 10</a>. For types that have no implicit casts to or from any
other types, it is sufficient to leave these settings at the defaults.
However, for a group of related types that have implicit casts, it is often
helpful to mark them all as belonging to a category and select one or two
of the <span class="quote">“<span class="quote">most general</span>”</span> types as being preferred within the category.
The <em class="replaceable"><code>category</code></em> parameter is
especially useful when adding a user-defined type to an existing built-in
category, such as the numeric or string types. However, it is also
possible to create new entirely-user-defined type categories. Select any
ASCII character other than an upper-case letter to name such a category.
</p><p>
A default value can be specified, in case a user wants columns of the
data type to default to something other than the null value.
Specify the default with the <code class="literal">DEFAULT</code> key word.
(Such a default can be overridden by an explicit <code class="literal">DEFAULT</code>
clause attached to a particular column.)
</p><p>
To indicate that a type is an array, specify the type of the array
elements using the <code class="literal">ELEMENT</code> key word. For example, to
define an array of 4-byte integers (<code class="type">int4</code>), specify
<code class="literal">ELEMENT = int4</code>. More details about array types
appear below.
</p><p>
To indicate the delimiter to be used between values in the external
representation of arrays of this type, <em class="replaceable"><code>delimiter</code></em> can be
set to a specific character. The default delimiter is the comma
(<code class="literal">,</code>). Note that the delimiter is associated
with the array element type, not the array type itself.
</p><p>
If the optional Boolean
parameter <em class="replaceable"><code>collatable</code></em>
is true, column definitions and expressions of the type may carry
collation information through use of
the <code class="literal">COLLATE</code> clause. It is up to the
implementations of the functions operating on the type to actually
make use of the collation information; this does not happen
automatically merely by marking the type collatable.
</p></div><div class="refsect2" id="id-1.9.3.94.5.9"><h3>Array Types</h3><p>
Whenever a user-defined type is created,
<span class="productname">PostgreSQL</span> automatically creates an
associated array type, whose name consists of the element type's
name prepended with an underscore, and truncated if necessary to keep
it less than <code class="symbol">NAMEDATALEN</code> bytes long. (If the name
so generated collides with an existing type name, the process is
repeated until a non-colliding name is found.)
This implicitly-created array type is variable length and uses the
built-in input and output functions <code class="literal">array_in</code> and
<code class="literal">array_out</code>. The array type tracks any changes in its
element type's owner or schema, and is dropped if the element type is.
</p><p>
You might reasonably ask why there is an <code class="option">ELEMENT</code>
option, if the system makes the correct array type automatically.
The only case where it's useful to use <code class="option">ELEMENT</code> is when you are
making a fixed-length type that happens to be internally an array of a number of
identical things, and you want to allow these things to be accessed
directly by subscripting, in addition to whatever operations you plan
to provide for the type as a whole. For example, type <code class="type">point</code>
is represented as just two floating-point numbers, which can be accessed
using <code class="literal">point[0]</code> and <code class="literal">point[1]</code>.
Note that
this facility only works for fixed-length types whose internal form
is exactly a sequence of identical fixed-length fields. A subscriptable
variable-length type must have the generalized internal representation
used by <code class="literal">array_in</code> and <code class="literal">array_out</code>.
For historical reasons (i.e., this is clearly wrong but it's far too
late to change it), subscripting of fixed-length array types starts from
zero, rather than from one as for variable-length arrays.
</p></div></div><div class="refsect1" id="id-1.9.3.94.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of a type to be created.
</p></dd><dt><span class="term"><em class="replaceable"><code>attribute_name</code></em></span></dt><dd><p>
The name of an attribute (column) for the composite type.
</p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p>
The name of an existing data type to become a column of the
composite type.
</p></dd><dt><span class="term"><em class="replaceable"><code>collation</code></em></span></dt><dd><p>
The name of an existing collation to be associated with a column of
a composite type, or with a range type.
</p></dd><dt><span class="term"><em class="replaceable"><code>label</code></em></span></dt><dd><p>
A string literal representing the textual label associated with
one value of an enum type.
</p></dd><dt><span class="term"><em class="replaceable"><code>subtype</code></em></span></dt><dd><p>
The name of the element type that the range type will represent ranges
of.
</p></dd><dt><span class="term"><em class="replaceable"><code>subtype_operator_class</code></em></span></dt><dd><p>
The name of a b-tree operator class for the subtype.
</p></dd><dt><span class="term"><em class="replaceable"><code>canonical_function</code></em></span></dt><dd><p>
The name of the canonicalization function for the range type.
</p></dd><dt><span class="term"><em class="replaceable"><code>subtype_diff_function</code></em></span></dt><dd><p>
The name of a difference function for the subtype.
</p></dd><dt><span class="term"><em class="replaceable"><code>input_function</code></em></span></dt><dd><p>
The name of a function that converts data from the type's
external textual form to its internal form.
</p></dd><dt><span class="term"><em class="replaceable"><code>output_function</code></em></span></dt><dd><p>
The name of a function that converts data from the type's
internal form to its external textual form.
</p></dd><dt><span class="term"><em class="replaceable"><code>receive_function</code></em></span></dt><dd><p>
The name of a function that converts data from the type's
external binary form to its internal form.
</p></dd><dt><span class="term"><em class="replaceable"><code>send_function</code></em></span></dt><dd><p>
The name of a function that converts data from the type's
internal form to its external binary form.
</p></dd><dt><span class="term"><em class="replaceable"><code>type_modifier_input_function</code></em></span></dt><dd><p>
The name of a function that converts an array of modifier(s) for the type
into internal form.
</p></dd><dt><span class="term"><em class="replaceable"><code>type_modifier_output_function</code></em></span></dt><dd><p>
The name of a function that converts the internal form of the type's
modifier(s) to external textual form.
</p></dd><dt><span class="term"><em class="replaceable"><code>analyze_function</code></em></span></dt><dd><p>
The name of a function that performs statistical analysis for the
data type.
</p></dd><dt><span class="term"><em class="replaceable"><code>internallength</code></em></span></dt><dd><p>
A numeric constant that specifies the length in bytes of the new
type's internal representation. The default assumption is that
it is variable-length.
</p></dd><dt><span class="term"><em class="replaceable"><code>alignment</code></em></span></dt><dd><p>
The storage alignment requirement of the data type. If specified,
it must be <code class="literal">char</code>, <code class="literal">int2</code>,
<code class="literal">int4</code>, or <code class="literal">double</code>; the
default is <code class="literal">int4</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>storage</code></em></span></dt><dd><p>
The storage strategy for the data type. If specified, must be
<code class="literal">plain</code>, <code class="literal">external</code>,
<code class="literal">extended</code>, or <code class="literal">main</code>; the
default is <code class="literal">plain</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>like_type</code></em></span></dt><dd><p>
The name of an existing data type that the new type will have the
same representation as. The values of
<em class="replaceable"><code>internallength</code></em>,
<em class="replaceable"><code>passedbyvalue</code></em>,
<em class="replaceable"><code>alignment</code></em>, and
<em class="replaceable"><code>storage</code></em>
are copied from that type, unless overridden by explicit
specification elsewhere in this <code class="command">CREATE TYPE</code> command.
</p></dd><dt><span class="term"><em class="replaceable"><code>category</code></em></span></dt><dd><p>
The category code (a single ASCII character) for this type.
The default is <code class="literal">'U'</code> for <span class="quote">“<span class="quote">user-defined type</span>”</span>.
Other standard category codes can be found in
<a class="xref" href="catalog-pg-type.html#CATALOG-TYPCATEGORY-TABLE" title="Table 52.63. typcategory Codes">Table 52.63</a>. You may also choose
other ASCII characters in order to create custom categories.
</p></dd><dt><span class="term"><em class="replaceable"><code>preferred</code></em></span></dt><dd><p>
True if this type is a preferred type within its type category,
else false. The default is false. Be very careful about creating
a new preferred type within an existing type category, as this
could cause surprising changes in behavior.
</p></dd><dt><span class="term"><em class="replaceable"><code>default</code></em></span></dt><dd><p>
The default value for the data type. If this is omitted, the
default is null.
</p></dd><dt><span class="term"><em class="replaceable"><code>element</code></em></span></dt><dd><p>
The type being created is an array; this specifies the type of
the array elements.
</p></dd><dt><span class="term"><em class="replaceable"><code>delimiter</code></em></span></dt><dd><p>
The delimiter character to be used between values in arrays made
of this type.
</p></dd><dt><span class="term"><em class="replaceable"><code>collatable</code></em></span></dt><dd><p>
True if this type's operations can use collation information.
The default is false.
</p></dd></dl></div></div><div class="refsect1" id="SQL-CREATETYPE-NOTES"><h2>Notes</h2><p>
Because there are no restrictions on use of a data type once it's been
created, creating a base type or range type is tantamount to granting
public execute permission on the functions mentioned in the type definition.
This is usually
not an issue for the sorts of functions that are useful in a type
definition. But you might want to think twice before designing a type
in a way that would require <span class="quote">“<span class="quote">secret</span>”</span> information to be used
while converting it to or from external form.
</p><p>
Before <span class="productname">PostgreSQL</span> version 8.3, the name of
a generated array type was always exactly the element type's name with one
underscore character (<code class="literal">_</code>) prepended. (Type names were
therefore restricted in length to one less character than other names.)
While this is still usually the case, the array type name may vary from
this in case of maximum-length names or collisions with user type names
that begin with underscore. Writing code that depends on this convention
is therefore deprecated. Instead, use
<code class="structname">pg_type</code>.<code class="structfield">typarray</code> to locate the array type
associated with a given type.
</p><p>
It may be advisable to avoid using type and table names that begin with
underscore. While the server will change generated array type names to
avoid collisions with user-given names, there is still risk of confusion,
particularly with old client software that may assume that type names
beginning with underscores always represent arrays.
</p><p>
Before <span class="productname">PostgreSQL</span> version 8.2, the shell-type
creation syntax
<code class="literal">CREATE TYPE <em class="replaceable"><code>name</code></em></code> did not exist.
The way to create a new base type was to create its input function first.
In this approach, <span class="productname">PostgreSQL</span> will first see
the name of the new data type as the return type of the input function.
The shell type is implicitly created in this situation, and then it
can be referenced in the definitions of the remaining I/O functions.
This approach still works, but is deprecated and might be disallowed in
some future release. Also, to avoid accidentally cluttering
the catalogs with shell types as a result of simple typos in function
definitions, a shell type will only be made this way when the input
function is written in C.
</p><p>
In <span class="productname">PostgreSQL</span> versions before 7.3, it
was customary to avoid creating a shell type at all, by replacing the
functions' forward references to the type name with the placeholder
pseudo-type <code class="type">opaque</code>. The <code class="type">cstring</code> arguments and
results also had to be declared as <code class="type">opaque</code> before 7.3. To
support loading of old dump files, <code class="command">CREATE TYPE</code> will
accept I/O functions declared using <code class="type">opaque</code>, but it will issue
a notice and change the function declarations to use the correct
types.
</p></div><div class="refsect1" id="id-1.9.3.94.8"><h2>Examples</h2><p>
This example creates a composite type and uses it in
a function definition:
</p><pre class="programlisting">
CREATE TYPE compfoo AS (f1 int, f2 text);
CREATE FUNCTION getfoo() RETURNS SETOF compfoo AS $$
SELECT fooid, fooname FROM foo
$$ LANGUAGE SQL;
</pre><p>
</p><p>
This example creates an enumerated type and uses it in
a table definition:
</p><pre class="programlisting">
CREATE TYPE bug_status AS ENUM ('new', 'open', 'closed');
CREATE TABLE bug (
id serial,
description text,
status bug_status
);
</pre><p>
</p><p>
This example creates a range type:
</p><pre class="programlisting">
CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi);
</pre><p>
</p><p>
This example creates the base data type <code class="type">box</code> and then uses the
type in a table definition:
</p><pre class="programlisting">
CREATE TYPE box;
CREATE FUNCTION my_box_in_function(cstring) RETURNS box AS ... ;
CREATE FUNCTION my_box_out_function(box) RETURNS cstring AS ... ;
CREATE TYPE box (
INTERNALLENGTH = 16,
INPUT = my_box_in_function,
OUTPUT = my_box_out_function
);
CREATE TABLE myboxes (
id integer,
description box
);
</pre><p>
</p><p>
If the internal structure of <code class="type">box</code> were an array of four
<code class="type">float4</code> elements, we might instead use:
</p><pre class="programlisting">
CREATE TYPE box (
INTERNALLENGTH = 16,
INPUT = my_box_in_function,
OUTPUT = my_box_out_function,
ELEMENT = float4
);
</pre><p>
which would allow a box value's component numbers to be accessed
by subscripting. Otherwise the type behaves the same as before.
</p><p>
This example creates a large object type and uses it in
a table definition:
</p><pre class="programlisting">
CREATE TYPE bigobj (
INPUT = lo_filein, OUTPUT = lo_fileout,
INTERNALLENGTH = VARIABLE
);
CREATE TABLE big_objs (
id integer,
obj bigobj
);
</pre><p>
</p><p>
More examples, including suitable input and output functions, are
in <a class="xref" href="xtypes.html" title="38.12. User-defined Types">Section 38.12</a>.
</p></div><div class="refsect1" id="SQL-CREATETYPE-COMPATIBILITY"><h2>Compatibility</h2><p>
The first form of the <code class="command">CREATE TYPE</code> command, which
creates a composite type, conforms to the <acronym class="acronym">SQL</acronym> standard.
The other forms are <span class="productname">PostgreSQL</span>
extensions. The <code class="command">CREATE TYPE</code> statement in
the <acronym class="acronym">SQL</acronym> standard also defines other forms that are not
implemented in <span class="productname">PostgreSQL</span>.
</p><p>
The ability to create a composite type with zero attributes is
a <span class="productname">PostgreSQL</span>-specific deviation from the
standard (analogous to the same case in <code class="command">CREATE TABLE</code>).
</p></div><div class="refsect1" id="SQL-CREATETYPE-SEE-ALSO"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-altertype.html" title="ALTER TYPE"><span class="refentrytitle">ALTER TYPE</span></a>, <a class="xref" href="sql-createdomain.html" title="CREATE DOMAIN"><span class="refentrytitle">CREATE DOMAIN</span></a>, <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a>, <a class="xref" href="sql-droptype.html" title="DROP TYPE"><span class="refentrytitle">DROP TYPE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createtrigger.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createuser.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE TRIGGER </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> CREATE USER</td></tr></table></div></body></html>
