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Nikita Glukhov
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Add documentation for JSON_TABLE
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‎doc/src/sgml/func.sgml

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<link linkend="functions-jsonquery"><literal>JSON_QUERY</literal></link>
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</para>
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</listitem>
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<listitem>
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<para>
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<xref linkend="functions-jsontable"/>
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</para>
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</listitem>
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</itemizedlist>
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<para>
@@ -18582,6 +18587,285 @@ FROM
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</sect5>
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</sect4>
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<refentry id="functions-jsontable">
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<refnamediv>
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<refname>JSON_TABLE</refname>
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<refpurpose>display JSON data as an SQL relation</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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JSON_TABLE (
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<replaceable class="parameter">json_api_common_syntax</replaceable>
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COLUMNS ( <replaceable class="parameter">json_table_column</replaceable> [, ...] )
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)
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<phrase>
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where <replaceable class="parameter">json_table_column</replaceable> is:
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</phrase>
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<replaceable>name</replaceable> <replaceable>type</replaceable> [ PATH <replaceable>json_path_specification</replaceable> ]
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[ { ERROR | NULL | DEFAULT expression } ON EMPTY ]
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[ { ERROR | NULL | DEFAULT expression } ON ERROR ]
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| <replaceable>name</replaceable> <replaceable>type</replaceable> FORMAT <replaceable>json_representation</replaceable>
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[ PATH <replaceable>json_path_specification</replaceable> ]
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[ { WITHOUT | WITH { CONDITIONAL | [UNCONDITIONAL] } }
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[ ARRAY ] WRAPPER ]
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[ { KEEP | OMIT } QUOTES [ ON SCALAR STRING ] ]
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[ { ERROR | NULL | EMPTY { ARRAY | OBJECT } } ON EMPTY ]
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[ { ERROR | NULL | EMPTY { ARRAY | OBJECT } } ON ERROR ]
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| NESTED PATH <replaceable>json_path_specification</replaceable> [ AS <replaceable>path_name</replaceable> ]
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COLUMNS ( <replaceable>json_table_column</replaceable> [, ...] )
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| <replaceable>name</replaceable> FOR ORDINALITY
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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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<function>JSON_TABLE</function> function queries <acronym>JSON</acronym> data
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and presents the results as a relational view, which can be accessed as a
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regular SQL table. You can only use <function>JSON_TABLE</function> inside the
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<literal>FROM</literal> clause of the <literal>SELECT</literal> statement
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for an SQL table.
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</para>
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<para>
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Taking JSON data as input, <function>JSON_TABLE</function> uses
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a path expression to extract a part of the provided data that
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will be used as a <firstterm>row pattern</firstterm> for the
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constructed view. Each SQL/JSON item at the top level of the row pattern serves
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as the source for a separate row in the constructed relational view.
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</para>
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<para>
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To split the row pattern into columns, <function>JSON_TABLE</function>
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provides the <literal>COLUMNS</literal> clause that defines the
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schema of the created view. For each column to be constructed,
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this clause provides a separate path expression that evaluates
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the row pattern, extracts a JSON item, and returns it as a
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separate SQL value for the specified column. If the required value
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is stored in a nested level of the row pattern, it can be extracted
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using the <literal>NESTED PATH</literal> subclause. Joining the
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columns returned by <literal>NESTED PATH</literal> can add multiple
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new rows to the constructed view. Such rows are called
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<firstterm>child rows</firstterm>, as opposed to the <firstterm>parent row</firstterm>
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that generates them.
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</para>
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<para>
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The rows produced by <function>JSON_TABLE</function> are laterally
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joined to the row that generated them, so you do not have to explicitly join
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the constructed view with the original table holding <acronym>JSON</acronym>
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data.
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</para>
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<para>
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Each <literal>NESTED PATH</literal> clause can generate one or more
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columns, which are considered to be <firstterm>siblings</firstterm>
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to each other. In relation to the columns returned directly from the row
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expression or by the <literal>NESTED PATH</literal> clause of a
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higher level, these columns are <firstterm>child</firstterm> columns.
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Sibling columns are always joined first. Once they are processed,
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the resulting rows are joined to the parent row.
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</para>
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<para>
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Columns with parent/child relationship are joined using
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<literal>LEFT OUTER JOIN</literal>, so that the parent row
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is always included into the output even if it does not have any child rows
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after joining the data returned by <literal>NESTED PATH</literal>,
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with NULL values inserted into the child columns if the corresponding
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values are missing.
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</para>
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<para>
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Sibling columns are joined using
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<literal>FULL OUTER JOIN ON FALSE</literal>, so that both parent and child
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rows are included into the output, with NULL values inserted
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into both child and parrent columns for all missing values.
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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">json_api_common_syntax</replaceable></literal>
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</term>
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<listitem>
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<para>
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The input data to query, the JSON path expression defining the query,
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and an optional <literal>PASSING</literal> clause, as described in
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<xref linkend="sqljson-input-clause"/>. The result of the input data
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evaluation is called the <firstterm>row pattern</firstterm>. The row
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pattern is used as the source for row values in the constructed view.
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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>COLUMNS( { <replaceable class="parameter">json_table_column</replaceable> } [, ...] )</literal>
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</term>
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<listitem>
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<para>
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The <literal>COLUMNS</literal> clause defining the schema of the
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constructed view. In this clause, you must specify all the columns
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to be filled with SQL/JSON items. Only scalar column types are supported.
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The <replaceable class="parameter">json_table_column</replaceable>
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expression has the following syntax variants:
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<literal><replaceable>name</replaceable> <replaceable>type</replaceable>
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[ PATH <replaceable>json_path_specification</replaceable> ]</literal>
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</term>
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<listitem>
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<para>
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Inserts a single SQL/JSON item into each row of
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the specified column.
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</para>
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<para>
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The provided <literal>PATH</literal> expression parses the
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row pattern defined by <replaceable>json_api_common_syntax</replaceable>
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and fills the column with produced SQL/JSON items, one for each row.
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If the <literal>PATH</literal> expression is omitted,
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<function>JSON_TABLE</function> uses the
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<literal>$.<replaceable>name</replaceable></literal> path expression,
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where <replaceable>name</replaceable> is the provided column name.
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In this case, the column name must correspond to one of the
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keys within the SQL/JSON item produced by the row pattern.
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</para>
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<para>
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Optionally, you can add <literal>ON EMPTY</literal> and
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<literal>ON ERROR</literal> clauses to define how to handle
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missing values or structural errors. These clauses have the same syntax
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and semantics as in <xref linkend="functions-jsonvalue"/>.
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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><replaceable>name</replaceable> <replaceable>type</replaceable> FORMAT <replaceable>json_representation</replaceable>
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[ PATH <replaceable>json_path_specification</replaceable> ]</literal>
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</term>
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<listitem>
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<para>
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Gerenates a column and inserts a composite SQL/JSON
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item into each row of this column.
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</para>
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<para>
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The provided <literal>PATH</literal> expression parses the
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row pattern defined by <replaceable>json_api_common_syntax</replaceable>
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and fills the column with produced SQL/JSON items, one for each row.
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If the <literal>PATH</literal> expression is omitted,
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<function>JSON_TABLE</function> uses the
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<literal>$.<replaceable>name</replaceable></literal> path expression,
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where <replaceable>name</replaceable> is the provided column name.
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In this case, the column name must correspond to one of the
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keys within the SQL/JSON item produced by the row pattern.
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</para>
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<para>
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Optionally, you can add <literal>WRAPPER</literal>, <literal>QUOTES</literal>,
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<literal>ON EMPTY</literal> and <literal>ON ERROR</literal> clauses
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to define additional settings for the returned SQL/JSON items.
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These clauses have the same syntax and semantics as
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in <xref linkend="functions-jsonquery"/>.
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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>NESTED PATH <replaceable>json_path_specification</replaceable> [ AS <replaceable>json_path_name</replaceable> ]
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COLUMNS ( <replaceable>json_table_column</replaceable> [, ...] )</literal>
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</term>
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<listitem>
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<para>
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Extracts SQL/JSON items from nested levels of the row pattern,
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gerenates one or more columns as defined by the <literal>COLUMNS</literal>
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subclause, and inserts the extracted SQL/JSON items into each row of these columns.
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The <replaceable>json_table_column</replaceable> expression in the
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<literal>COLUMNS</literal> subclause uses the same syntax as in the
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parent <literal>COLUMNS</literal> clause.
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</para>
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<para>
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The <literal>NESTED PATH</literal> syntax is recursive,
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so you can go down multiple nested levels by specifying several
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<literal>NESTED PATH</literal> subclauses within each other.
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It allows to unnest the hierarchy of JSON objects and arrays
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in a single function invocation rather than chaining several
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<function>JSON_TABLE</function> expressions in an SQL statement.
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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><replaceable>name</replaceable> FOR ORDINALITY</literal>
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</term>
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<listitem>
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<para>
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Adds an ordinality column that provides sequential row numbering.
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You can have only one ordinality column per table. Row numbering
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is 1-based. For child rows that result from the <literal>NESTED PATH</literal>
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clauses, the parent row number is repeated.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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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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Query the <structname>my_films</structname> table holding
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some JSON data about the films and create a view that
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distributes the film genre, title, and director between separate columns:
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<screen>
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SELECT jt.* FROM
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my_films,
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JSON_TABLE ( js, '$.favorites[*]' COLUMNS (
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id FOR ORDINALITY,
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kind text PATH '$.kind',
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NESTED PATH '$.films[*]' COLUMNS (
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title text PATH '$.title',
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director text PATH '$.director'))) AS jt;
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----+----------+------------------+-------------------
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id | kind | title | director
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----+----------+------------------+-------------------
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1 | comedy | Bananas | Woody Allen
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1 | comedy | The Dinner Game | Francis Veber
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2 | horror | Psycho | Alfred Hitchcock
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3 | thriller | Vertigo | Hitchcock
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4 | drama | Yojimbo | Akira Kurosawa
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(5 rows)
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</screen>
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</para>
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</refsect1>
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</refentry>
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</sect3>
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