diff options
Diffstat (limited to 'doc/src/sgml/ref')
| -rw-r--r-- | doc/src/sgml/ref/create_type.sgml | 50 |
1 files changed, 49 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/create_type.sgml b/doc/src/sgml/ref/create_type.sgml index e643f098252..8002e2c4b9c 100644 --- a/doc/src/sgml/ref/create_type.sgml +++ b/doc/src/sgml/ref/create_type.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.74 2008/05/27 18:05:13 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.75 2008/07/30 17:05:04 tgl Exp $ PostgreSQL documentation --> @@ -38,6 +38,8 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> ( [ , PASSEDBYVALUE ] [ , ALIGNMENT = <replaceable class="parameter">alignment</replaceable> ] [ , STORAGE = <replaceable class="parameter">storage</replaceable> ] + [ , CATEGORY = <replaceable class="parameter">category</replaceable> ] + [ , PREFERRED = <replaceable class="parameter">preferred</replaceable> ] [ , DEFAULT = <replaceable class="parameter">default</replaceable> ] [ , ELEMENT = <replaceable class="parameter">element</replaceable> ] [ , DELIMITER = <replaceable class="parameter">delimiter</replaceable> ] @@ -282,6 +284,27 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> </para> <para> + The <replaceable class="parameter">category</replaceable> and + <replaceable class="parameter">preferred</replaceable> 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 <quote>preferred</> 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 <xref + linkend="typeconv">. 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 <quote>most general</> types as being preferred within the category. + The <replaceable class="parameter">category</replaceable> 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. + </para> + + <para> 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 <literal>DEFAULT</literal> key word. @@ -495,6 +518,31 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> </varlistentry> <varlistentry> + <term><replaceable class="parameter">category</replaceable></term> + <listitem> + <para> + The category code (a single ASCII character) for this type. + The default is <literal>'U'</> for <quote>user-defined type</>. + Other standard category codes can be found in + <xref linkend="catalog-typcategory-table">. You may also choose + other ASCII characters in order to create custom categories. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">preferred</replaceable></term> + <listitem> + <para> + True if this type is a preferred type within its type category, + else false. The default is true (which is appropriate for + all entries in category <literal>U</>, but is usually not + appropriate for new types in other categories — beware!). + </para> + </listitem> + </varlistentry> + + <varlistentry> <term><replaceable class="parameter">default</replaceable></term> <listitem> <para> |