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Some more editing of the range-types documentation.

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Be more thorough about specifying the expectations for canonical and
subtype_diff functions, and move that info to the same place.
This commit is contained in:
Tom Lane
2011-11-23 19:13:56 -05:00
parent b7056b8324
commit 604d4c4c95
2 changed files with 98 additions and 47 deletions
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29
doc/src/sgml/ref/create_type.sgml
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@@ -128,9 +128,9 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
<para>
The range type's <replaceable class="parameter">subtype</replaceable> can
be any type with an associated btree operator class (to determine the
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
btree operator class is used to determine ordering; to use a non-default
b-tree operator class is used to determine ordering; to use a non-default
opclass, specify its name with <replaceable
class="parameter">subtype_opclass</replaceable>. If the subtype is
collatable, and you want to use a non-default collation in the range's
@@ -141,16 +141,18 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
<para>
The optional <replaceable class="parameter">canonical</replaceable>
function must take one argument of the range type being defined, and
return a value of the same type. This is used to convert the range value
to a canonical form, when applicable. See <xref linkend="rangetypes">
for more information. To define
the <replaceable class="parameter">canonical</replaceable> function,
you must first create a shell type, which is a
return a value of the same type. This is used to convert range values
to a canonical form, when applicable. See <xref
linkend="rangetypes-defining"> for more information. Creating a
<replaceable class="parameter">canonical</replaceable> 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 <literal>CREATE TYPE
<replaceable>name</></literal>, with no additional parameters. Then
the function can be declared, and finally the range type can be declared,
replacing the shell type entry with a valid range type.
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.
</para>
<para>
@@ -160,11 +162,8 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
and return a <type>double precision</type> 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. Note that the <replaceable
class="parameter">subtype_diff</replaceable> function should agree with
the sort ordering implied by the selected operator class and collation;
that is, its result should be positive whenever its first argument is
greater than its second according to the sort ordering.
the range type. See <xref linkend="rangetypes-defining"> for more
information.
</para>
</refsect2>
@@ -541,7 +540,7 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
<term><replaceable class="parameter">subtype_operator_class</replaceable></term>
<listitem>
<para>
The name of a btree operator class for the subtype.
The name of a b-tree operator class for the subtype.
</para>
</listitem>
</varlistentry>