Re: remaining sql/json patches - Mailing list pgsql-hackers

On Thu, Jan 25, 2024 at 10:39 PM jian he <jian.universality@gmail.com> wrote:
>
> On Thu, Jan 25, 2024 at 7:54 PM Amit Langote <amitlangote09@gmail.com> wrote:
> >
> > >
> > > The problem with returning comp_domain_with_typmod from json_value()
> > > seems to be that it's using a text-to-record CoerceViaIO expression
> > > picked from JsonExpr.item_coercions, which behaves differently than
> > > the expression tree that the following uses:
> > >
> > > select ('abcd', 42)::comp_domain_with_typmod;
> > >    row
> > > ----------
> > >  (abc,42)
> > > (1 row)
> >
> > Oh, it hadn't occurred to me to check what trying to coerce a "string"
> > containing the record literal would do:
> >
> > select '(''abcd'', 42)'::comp_domain_with_typmod;
> > ERROR:  value too long for type character(3)
> > LINE 1: select '(''abcd'', 42)'::comp_domain_with_typmod;
> >
> > which is the same thing as what the JSON_QUERY() and JSON_VALUE() are
> > running into.  So, it might be fair to think that the error is not a
> > limitation of the SQL/JSON patch but an underlying behavior that it
> > has to accept as is.
> >
>
> Hi, I reconciled with these cases.
> What bugs me now is the first query of the following 4 cases (for comparison).
> SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING char(3) omit quotes);
> SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING char(3) keep quotes);
> SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING text omit quotes);
> SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING text keep quotes);
>

based on v39.
in ExecEvalJsonCoercion
coercion->targettypmod related function calls:
json_populate_type calls populate_record_field, then populate_scalar,
later will eventually call InputFunctionCallSafe.

so I make the following change:
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -4533,7 +4533,7 @@ ExecEvalJsonCoercion(ExprState *state, ExprEvalStep *op,
         * deed ourselves by calling the input function, that is, after removing
         * the quotes.
         */
-       if (jb && JB_ROOT_IS_SCALAR(jb) && coercion->omit_quotes)
+       if ((jb && JB_ROOT_IS_SCALAR(jb) && coercion->omit_quotes) ||
coercion->targettypmod != -1)

now the following two return the same result:  `[1,`
SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING char(3) omit quotes);
SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING char(3) keep quotes);