Horton

Re: pgsql: Add more SQL/JSON constructor functions

jian he <jian.universality@gmail.com>

View thread View on postgr.es
From: jian he <jian.universality@gmail.com>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Peter Eisentraut <peter@eisentraut.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-09-03T09:05:02Z
Lists: pgsql-hackers 
On Mon, Sep 2, 2024 at 4:18 PM Amit Langote <amitlangote09@gmail.com> wrote:
>
> > See 0001.
> >

> >
> > See 0002.
> >
> > I'm also attaching 0003 to fix a minor annoyance that JSON_TABLE()
> > columns' default ON ERROR, ON EMPTY behaviors are unnecessarily
> > emitted in the deparsed output when the top-level ON ERROR behavior is
> > ERROR.
> >
> > Will push these on Monday.



v2-0001 looks good to me.

+-- Test JSON_TABLE() column deparsing -- don't emit default ON ERROR / EMPTY
+-- behavior
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$'));
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text
PATH '$') ERROR ON ERROR);

Are these tests duplicated? appears both in v2-0002 and v2-0003.


0002 output is:
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text
PATH '$') ERROR ON ERROR);
+
QUERY PLAN
+------------------------------------------------------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS
json_table_path_0 COLUMNS (a text PATH '$' NULL ON EMPTY NULL ON
ERROR) ERROR ON ERROR)
+(3 rows)

0003 output is:
EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text
PATH '$') ERROR ON ERROR);
                                                     QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
 Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
   Output: a
   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS
json_table_path_0 COLUMNS (a text PATH '$') ERROR ON ERROR)
(3 rows)

two patches with different output,
overall we should merge 0002 and 0003?



    if (jsexpr->on_error &&
        jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
        (jsexpr->on_error->btype != JSON_BEHAVIOR_NULL || returning_domain))

we can be simplified as
      if ( jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
         (jsexpr->on_error->btype != JSON_BEHAVIOR_NULL || returning_domain))

since if jsexpr->on_error is NULL, then segfault will appear at the beginning of
ExecInitJsonExpr


+ *
+ * Only add the extra steps for a NULL-valued expression when RETURNING a
+ * domain type to check the constraints, if any.
  */
+ jsestate->jump_error = state->steps_len;
  if (jsexpr->on_error &&
- jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
+ jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
+ (jsexpr->on_error->btype != JSON_BEHAVIOR_NULL || returning_domain))

+ *
+ * Only add the extra steps for a NULL-valued expression when RETURNING a
+ * domain type to check the constraints, if any.
  */
+ jsestate->jump_empty = state->steps_len;
  if (jsexpr->on_empty != NULL &&
- jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR)
+ jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR &&
+ (jsexpr->on_empty->btype != JSON_BEHAVIOR_NULL || returning_domain))

I am a little bit confused with the comments.
not sure the "NULL-valued expression" refers to.

i think it is:
implicitly default for ON EMPTY | ERROR clause is NULL (JSON_BEHAVIOR_NULL)
for that situation, we can skip the json coercion process,
but this only applies when the returning type of JsonExpr is not domain,

Commits

  1. SQL/JSON: Avoid initializing unnecessary ON ERROR / ON EMPTY steps

  2. SQL/JSON: Fix default ON ERROR behavior for JSON_TABLE

  3. SQL/JSON: Fix JSON_TABLE() column deparsing

  4. Update comment about ExprState.escontext

  5. SQL/JSON: Fix casting for integer EXISTS columns in JSON_TABLE

  6. SQL/JSON: Some fixes to JsonBehavior expression casting

  7. SQL/JSON: Remove useless code in ExecInitJsonExpr()

  8. SQL/JSON: Respect OMIT QUOTES when RETURNING domains over jsonb

  9. SQL/JSON: Improve error-handling of JsonBehavior expressions

  10. SQL/JSON: Fix error-handling of some JsonBehavior expressions

  11. SQL/JSON: Rethink c2d93c3802b

  12. SQL/JSON: Always coerce JsonExpr result at runtime

  13. SQL/JSON: Fix coercion of constructor outputs to types with typmod