Re: pgsql: Add more SQL/JSON constructor functions

On Thu, Aug 22, 2024 at 12:44 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Thu, Aug 22, 2024 at 11:02 jian he <jian(dot)universality(at)gmail(dot)com> wrote:
>> On Tue, Jul 30, 2024 at 12:59 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
>> > On Fri, Jul 26, 2024 at 11:19 PM jian he <jian(dot)universality(at)gmail(dot)com> wrote:
>> > > {
>> > > ...
>> > > /*
>> > > * For expression nodes that support soft errors. Should be set to NULL
>> > > * before calling ExecInitExprRec() if the caller wants errors thrown.
>> > > */
>> > > ErrorSaveContext *escontext;
>> > > } ExprState;
>> > >
>> > > i believe by default makeNode will set escontext to NULL.
>> > > So the comment should be, if you want to catch the soft errors, make
>> > > sure the escontext pointing to an allocated ErrorSaveContext.
>> > > or maybe just say, default is NULL.
>> > >
>> > > Otherwise, the original comment's meaning feels like: we need to
>> > > explicitly set it to NULL
>> > > for certain operations, which I believe is false?
>> >
>> > OK, I'll look into updating this.

See 0001.

>> > > json_behavior_type:
>> > > ERROR_P { $$ = JSON_BEHAVIOR_ERROR; }
>> > > | NULL_P { $$ = JSON_BEHAVIOR_NULL; }
>> > > | TRUE_P { $$ = JSON_BEHAVIOR_TRUE; }
>> > > | FALSE_P { $$ = JSON_BEHAVIOR_FALSE; }
>> > > | UNKNOWN { $$ = JSON_BEHAVIOR_UNKNOWN; }
>> > > | EMPTY_P ARRAY { $$ = JSON_BEHAVIOR_EMPTY_ARRAY; }
>> > > | EMPTY_P OBJECT_P { $$ = JSON_BEHAVIOR_EMPTY_OBJECT; }
>> > > /* non-standard, for Oracle compatibility only */
>> > > | EMPTY_P { $$ = JSON_BEHAVIOR_EMPTY_ARRAY; }
>> > > ;
>> > >
>> > > EMPTY_P behaves the same as EMPTY_P ARRAY
>> > > so for function GetJsonBehaviorConst, the following "case
>> > > JSON_BEHAVIOR_EMPTY:" is wrong?
>> > >
>> > > case JSON_BEHAVIOR_NULL:
>> > > case JSON_BEHAVIOR_UNKNOWN:
>> > > case JSON_BEHAVIOR_EMPTY:
>> > > val = (Datum) 0;
>> > > isnull = true;
>> > > typid = INT4OID;
>> > > len = sizeof(int32);
>> > > isbyval = true;
>> > > break;
>> > >
>> > > also src/backend/utils/adt/ruleutils.c
>> > > if (jexpr->on_error->btype != JSON_BEHAVIOR_EMPTY)
>> > > get_json_behavior(jexpr->on_error, context, "ERROR");
>> >
>> > Something like the attached makes sense? While this meaningfully
>> > changes the deparsing output, there is no behavior change for
>> > JsonTable top-level path execution. That's because the behavior when
>> > there's an error in the execution of the top-level path is to throw it
>> > or return an empty set, which is handled in jsonpath_exec.c, not
>> > execExprInterp.c.

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.

I haven't had a chance to take a closer look at your patch to optimize
the code in ExecInitJsonExpr() yet.

--
Thanks, Amit Langote