Re: SQL:2023 JSON simplified accessor support - Mailing list pgsql-hackers

On Sat, Aug 23, 2025 at 3:34 AM Alexandra Wang
<alexandra.wang.oss@gmail.com> wrote:
>
> I don’t understand the question. In the case of an unsupported Node
> type (not an Indices in patch 0001 or 0002), we break out of the loop
> to stop transforming the remaining subscripts. So there won’t be any
> ‘not contiguous’ indirection elements.
>

Sorry, my last message is wrong.
this time, I applied v13-0001 to v13-0005.
and I found some minor issues.....

v13-0002-Allow-Generic-Type-Subscripting-to-Accept-Dot-No.patch
+ /*
+ * Error out, if datatype failed to consume any indirection elements.
+ */
+ if (list_length(*indirection) == indirection_length)
+ {
+ Node   *ind = linitial(*indirection);
+
+ if (noError)
+ return NULL;
+
+ if (IsA(ind, String))
+ ereport(ERROR,
+ (errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("type %s does not support dot notation",
+ format_type_be(containerType)),
+ parser_errposition(pstate, exprLocation(containerBase))));
+ else if (IsA(ind, A_Indices))
+ ereport(ERROR,
+ (errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("type %s does not support array subscripting",
+ format_type_be(containerType)),
+ parser_errposition(pstate, exprLocation(containerBase))));
+ else
+ elog(ERROR, "invalid indirection operation: %d", nodeTag(ind));
+ }

these error message still not reached after I apply
v13-0005-Implement-read-only-dot-notation-for-jsonb.patch
maybe we can simply do

+ if (noError)
+ return NULL;
+
+ ereport(ERROR,
+ errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("type %s does not support subscripting",
+ format_type_be(containerType)),
+ parser_errposition(pstate, exprLocation(containerBase)));
?

for V13-0004.
in master we have
            if (subExpr == NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("jsonb subscript must have text type"),
                         parser_errposition(pstate, exprLocation(subExpr))));
but this part is removed from v13-0004-Extract-coerce_jsonpath_subscript
?

coerce_jsonpath_subscript_to_int4_or_text
maybe we can just rename to
coerce_jsonpath_subscript,
then add some comments explaining why currently only support result node coerce
to text or int4 data type.

for v13-0005-Implement-read-only-dot-notation-for-jsonb.patch

+ i = 0;
+ foreach(lc, sbsref->refupperindexpr) {
+ Expr *e = (Expr *) lfirst(lc);
+
+ /* When slicing, individual subscript bounds can be omitted */
+ if (!e) {
+ sbsrefstate->upperprovided[i] = false;
+ sbsrefstate->upperindexnull[i] = true;
+ } else {
+ sbsrefstate->upperprovided[i] = true;
+ /* Each subscript is evaluated into appropriate array entry */
+ ExecInitExprRec(e, state,
+ &sbsrefstate->upperindex[i],
+ &sbsrefstate->upperindexnull[i]);
+ }
+ i++;
  }
curly braces should be put into the next new line.

there are two
+ if (!sbsref->refjsonbpath)
+{
+}
maybe we can put these two together.

+SELECT (jb)['b']['x'].z FROM test_jsonb_dot_notation; -- returns NULL
with warnings
+ z
+---
+
+(1 row)
there is no warning, "returns NULL with warnings" should be removed.

+-- clean up
+DROP TABLE test_jsonb_dot_notation;
\ No newline at end of file

to remove "\ No newline at end of file"
you need to add a newline to jsonb.sql, you may see other regress sql
test files.

+ foreach(lc, *indirection)
+ if()
+ {
+ }
+ else
+ {
+ /*
+ * Unexpected node type in indirection list. This should not
+ * happen with current grammar, but we handle it defensively by
+ * breaking out of the loop rather than crashing. In case of
+ * future grammar changes that might introduce new node types,
+ * this allows us to create a jsonpath from as many indirection
+ * elements as we can and let transformIndirection() fallback to
+ * alternative logic to handle the remaining indirection elements.
+ */
+ Assert(false); /* not reachable */
+ break;
+ }
+
+ /* append path item */
+ path->next = jpi;
+ path = jpi;
+ pathlen++;

If the above else branch is reached, it will crash due to `Assert(false);`,
which contradicts the preceding comments.
to make the comments accurate, we need remove
" Assert(false); /* not reachable */"
?

  /*
- * Transform and convert the subscript expressions. Jsonb subscripting
- * does not support slices, look only at the upper index.
+ * We would only reach here if json simplified accessor is not needed, or
+ * if jsonb_subscript_make_jsonpath() didn't consume any indirection
+ * element — either way, the first indirection element could not be
+ * converted into a JsonPath component. This happens when it's a non-slice
+ * A_Indices with a non-integer upper index. The code below falls back to
+ * traditional jsonb subscripting for such cases.
  */
the above comments, "non-integer" part is wrong?
For example, the below two SELECTs both use "traditional" jsonb
subscripting logic.
CREATE TABLE ts1 AS SELECT '[1, [2]]' ::jsonb jb;
SELECT (jb)[1] FROM ts1;
SELECT (jb)['a'] FROM ts1;