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Nikita Glukhov
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Add documentation for IS JSON predicate
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‎doc/src/sgml/func.sgml

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@@ -16886,7 +16886,16 @@ $ ? (@ like_regex "^\\d+$")
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</listitem>
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</itemizedlist>
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<sect3 id="functions-sqljson-producing">
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<para>
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All SQL/JSON functions fall into one of the two groups.
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<link linkend="functions-sqljson-producing">Constructor functions</link>
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generate JSON data from values of SQL types.
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<link linkend="functions-sqljson-querying">Query functions</link>
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evaluate SQL/JSON path language expressions against JSON values
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and produce values of SQL/JSON types, which are converted to SQL types.
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</para>
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<sect3 id="functions-sqljson-producing">
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<title>Producing JSON Content</title>
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<para>
@@ -17646,10 +17655,254 @@ FROM films AS f;
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</sect5>
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</sect4>
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</sect3>
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<sect3 id="functions-sqljson-querying">
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<title>Querying JSON</title>
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<para>
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SQL/JSON query functions evaluate SQL/JSON path language expressions
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against JSON values, producing values of SQL/JSON types, which are
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converted to SQL types. All SQL/JSON query functions accept several
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common clauses described in <xref linkend="sqljson-common-clauses"/>.
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For details on the SQL/JSON path language,
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see <xref linkend="functions-sqljson-path"/>.
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<xref linkend="functions-isjson-predicate"/>
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</para>
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</listitem>
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</itemizedlist>
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<para>
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In some usage examples for these functions,
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the following small table storing some JSON data will be used:
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<programlisting>
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CREATE TABLE my_films (
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js text );
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INSERT INTO my_films VALUES (
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'{ "favorites" : [
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{ "kind" : "comedy", "films" : [
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{ "title" : "Bananas",
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"director" : "Woody Allen"},
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{ "title" : "The Dinner Game",
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"director" : "Francis Veber" } ] },
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{ "kind" : "horror", "films" : [
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{ "title" : "Psycho",
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"director" : "Alfred Hitchcock" } ] },
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{ "kind" : "thriller", "films" : [
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{ "title" : "Vertigo",
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"director" : "Alfred Hitchcock" } ] },
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{ "kind" : "drama", "films" : [
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{ "title" : "Yojimbo",
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"director" : "Akira Kurosawa" } ] }
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] }');
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</programlisting>
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</para>
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<refentry id="functions-isjson-predicate">
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<refnamediv>
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<refname>IS JSON</refname>
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<refpurpose>test whether the provided value is valid JSON data</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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<replaceable class="parameter">expression</replaceable>
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IS [ NOT ] JSON
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[ { VALUE | SCALAR | ARRAY | OBJECT } ]
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[ { WITH | WITHOUT } UNIQUE [ KEYS ] ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>IS JSON</command> predicate tests whether the provided value is valid
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<acronym>JSON</acronym> data. If you provide a specific JSON data type as a parameter,
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you can check whether the value belongs to this type.
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You can also use this predicate in the <command>IS NOT JSON</command> form.
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The return values are:
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<itemizedlist>
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<listitem>
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<para>
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<literal>t</literal> if the value satisfies the specified condition.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>f</literal> if the value does not satisfy the specified condition.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term>
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<literal><replaceable class="parameter">expression</replaceable></literal>
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</term>
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<listitem>
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<para>
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The input clause defining the value to test. You can provide the values
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of <literal>json</literal>, <literal>jsonb</literal>,
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<literal>bytea</literal>, or character string types.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>VALUE | SCALAR | ARRAY | OBJECT</literal>
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</term>
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<listitem>
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<para>
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Specifies the <acronym>JSON</acronym> data type to test for:
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<itemizedlist>
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<listitem>
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<para>
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<literal>VALUE</literal> (default) &mdash; any <acronym>JSON</acronym> type.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>SCALAR</literal> &mdash; <acronym>JSON</acronym> number, string, or boolean.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>ARRAY</literal> &mdash; <acronym>JSON</acronym> array.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>OBJECT</literal> &mdash; <acronym>JSON</acronym> object.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>{ WITH | WITHOUT } UNIQUE [ KEYS ]</literal>
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</term>
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<listitem>
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<para>Defines whether duplicate keys are allowed:
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<itemizedlist>
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<listitem>
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<para>
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<literal>WITHOUT</literal> (default) &mdash; the
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<acronym>JSON</acronym> object can contain duplicate keys.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>WITH</literal> &mdash; duplicate keys are not allowed.
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If the input data contains duplicate keys, it is considered to be invalid JSON.
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</para>
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</listitem>
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</itemizedlist>
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Optionally, you can add the <literal>KEYS</literal> keyword for semantic clarity.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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Compare the result returned by the <function>IS JSON</function>
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predicate for different data types:
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</para>
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<screen>
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SELECT
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js,
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js IS JSON "is json",
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js IS NOT JSON "is not json",
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js IS JSON SCALAR "is scalar",
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js IS JSON OBJECT "is object",
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js IS JSON ARRAY "is array"
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FROM
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(VALUES ('123'), ('"abc"'), ('{"a": "b"}'), ('[1,2]'), ('abc')) foo(js);
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js | is json | is not json | is scalar | is object | is array
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------------+---------+-------------+-----------+-----------|-------------
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123 | t | f | t | f | f
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"abc" | t | f | t | f | f
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{"a": "b"} | t | f | f | t | f
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[1,2] | t | f | f | f | t
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abc | f | t | f | f | f
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(5 rows)
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</screen>
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</refsect1>
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</refentry>
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</sect3>
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<sect3 id="sqljson-common-clauses">
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<title>SQL/JSON Common Clauses</title>
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<sect4 id="sqljson-input-clause">
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<title>SQL/JSON Input Clause</title>
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<variablelist>
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<varlistentry>
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<term>
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<literal><replaceable>context_item</replaceable>, <replaceable>path_expression</replaceable>
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[ PASSING { <replaceable>value</replaceable> AS <replaceable>varname</replaceable> } [, ...]]</literal>
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</term>
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<listitem>
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<para>
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The input clause specifies the JSON data to query and
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the exact query path to be passed to SQL/JSON query functions:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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The <replaceable>context_item</replaceable> is the JSON data to query.
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</para>
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</listitem>
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<listitem>
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<para>
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The <replaceable>path_expression</replaceable> is an SQL/JSON path
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expression that specifies the items to be retrieved from the JSON
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data. For details on path expression syntax, see
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<xref linkend="functions-sqljson-path"/>.
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</para>
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</listitem>
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<listitem>
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<para>
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The optional <command>PASSING</command> clause provides the values for
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the named variables used in the SQL/JSON path expression.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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The input clause is common for all SQL/JSON query functions.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect4>
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<sect4 id="sqljson-output-clause">
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<title>SQL/JSON Output Clause</title>
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