Re: remaining sql/json patches

some more minor issues:
SELECT * FROM JSON_TABLE(jsonb '{"a":[123,2]}', '$'
COLUMNS (item int[] PATH '$.a' error on error, foo text path '$'
error on error)) bar;
ERROR: JSON path expression in JSON_VALUE should return singleton scalar item

the error message seems not so great, imho.
since the JSON_TABLE doc entries didn't mention that
JSON_TABLE actually transformed to json_value, json_query, json_exists.

JSON_VALUE even though cannot specify KEEP | OMIT QUOTES.
It might be a good idea to mention the default is to omit quotes in the doc.
because JSON_TABLE actually transformed to json_value, json_query, json_exists.
JSON_TABLE can specify quotes behavior freely.

bother again, i kind of get what the function transformJsonTableChildPlan do,
but adding more comments would make it easier to understand....

(json_query)
+ This function must return a JSON string, so if the path expression
+ returns multiple SQL/JSON items, you must wrap the result using the
+ <literal>WITH WRAPPER</literal> clause. If the wrapper is
+ <literal>UNCONDITIONAL</literal>, an array wrapper will always
+ be applied, even if the returned value is already a single JSON object
+ or an array, but if it is <literal>CONDITIONAL</literal>, it
will not be
+ applied to a single array or object. <literal>UNCONDITIONAL</literal>
+ is the default. If the result is a scalar string, by default the value
+ returned will have surrounding quotes making it a valid JSON value,
+ which can be made explicit by specifying <literal>KEEP
QUOTES</literal>.
+ Conversely, quotes can be omitted by specifying <literal>OMIT
QUOTES</literal>.
+ The returned <replaceable>data_type</replaceable> has the
same semantics
+ as for constructor functions like <function>json_objectagg</function>;
+ the default returned type is <type>jsonb</type>.

+ <para>
+ Returns the result of applying the
+ <replaceable>path_expression</replaceable> to the
+ <replaceable>context_item</replaceable> using the
+ <literal>PASSING</literal> <replaceable>value</replaceable>s. The
+ extracted value must be a single <acronym>SQL/JSON</acronym> scalar
+ item. For results that are objects or arrays, use the
+ <function>json_query</function> function instead.
+ The returned <replaceable>data_type</replaceable> has the
same semantics
+ as for constructor functions like <function>json_objectagg</function>.
+ The default returned type is <type>text</type>.
+ The <literal>ON ERROR</literal> and <literal>ON EMPTY</literal>
+ clauses have similar semantics as mentioned in the description of
+ <function>json_query</function>.
+ </para>

+ The returned <replaceable>data_type</replaceable> has the
same semantics
+ as for constructor functions like <function>json_objectagg</function>.

IMHO, the above description is not so good, since the function
json_objectagg is listed in functions-aggregate.html,
using Ctrl + F in the browser cannot find json_objectagg in functions-json.html.

for json_query, maybe we can rephrase like:
the RETURNING clause, which specifies the data type returned. It must
be a type for which there is a cast from text to that type.
By default, the <type>jsonb</type> type is returned.

json_value:
the RETURNING clause, which specifies the data type returned. It must
be a type for which there is a cast from text to that type.
By default, the <type>text</type> type is returned.