</para></entry>

</row>

<row>

<entry><structfield>typsubscription</structfield></entry>

<entry><type>regproc</type></entry>

<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>

<entry>Custom subscription function with type-specific logic, or 0 if this type doesn't support subscription.</entry>

</row>

<row>

<entry><structfield>typdefaultbin</structfield></entry>

<entry><type>pg_node_tree</type></entry>

compared using the default database collation.

</para>

</sect2>

<sect2 id="json-subscription">

<title>JSON subscription</title>

<para>

JSONB data type support array-style subscription expressions to extract or update particular element. An example of subscription syntax:

<programlisting>

-- Extract value by key

SELECT ('{"a": 1}'::jsonb)['a'];

-- Extract nested value by key path

SELECT ('{"a": {"b": {"c": 1}}}'::jsonb)['a']['b']['c'];

-- Extract element by index

SELECT ('[1, "2", null]'::jsonb)['1'];

-- Update value by key

UPDATE table_name set jsonb_field['key'] = 1;

-- Select records using where clause with subscription

SELECT * from table_name where jsonb_field['key'] = '"value"';

</programlisting>

</para>

</sect2>

</sect1>

[ , ELEMENT = <replaceable class="parameter">element</replaceable> ]

[ , DELIMITER = <replaceable class="parameter">delimiter</replaceable> ]

[ , COLLATABLE = <replaceable class="parameter">collatable</replaceable> ]

[ , SUBSCRIPTION = <replaceable class="parameter">subscription_function</replaceable> ]

)

CREATE TYPE <replaceable class="parameter">name</replaceable>

<replaceable class="parameter">send_function</replaceable>,

<replaceable class="parameter">type_modifier_input_function</replaceable>,

<replaceable class="parameter">type_modifier_output_function</replaceable> and

<replaceable class="parameter">analyze_function</replaceable>

<replaceable class="parameter">analyze_function</replaceable>,

<replaceable class="parameter">subscription_function</replaceable>

are optional. Generally these functions have to be coded in C

or another low-level language.

</para>

make use of the collation information; this does not happen

automatically merely by marking the type collatable.

</para>

<para>

The optional

<replaceable class="parameter">subscription_function</replaceable>

contains type-specific logic for subscription of the data type.

By default, there is no such function, which means that the data

type doesn't support subscription. The subscription function must be

declared to take a single argument of type <type>internal</>, and return

a <type>internal</> result. There are two examples of implementation for

subscription function in case of array

(<replaceable class="parameter">array_subscription</replaceable>)

and jsonb

(<replaceable class="parameter">jsonb_subscription</replaceable>)

types in <filename>src/backend/utils/adt/arrayfuncs.c</> and

<filename>src/backend/utils/adt/jsonfuncs.c</> corresponding.

</para>

</refsect2>

<refsect2>

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><replaceable class="parameter">subscription_function</replaceable></term>

<listitem>

<para>

The name of a function that contains type-specific subscription logic for

the data type.

</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>