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

--- a/src/backend/parser/parse_node.c

+++ b/src/backend/parser/parse_node.c

@@ -244,7 +244,7 @@ transformContainerSubscripts(ParseState *pstate,

                                                         Node *containerBase,

                                                         Oid containerType,

                                                         int32 containerTypMod,

-                                                        List *indirection,

+                                                        List **indirection,

                                                         bool isAssignment)

 {

        SubscriptingRef *sbsref;

@@ -280,7 +280,7 @@ transformContainerSubscripts(ParseState *pstate,

         * element.  If any of the items are slice specifiers (lower:upper), then

         * the subscript expression means a container slice operation.

         */

-       foreach(idx, indirection)

+       foreach(idx, *indirection)

        {

                A_Indices  *ai = lfirst_node(A_Indices, idx);

Should this foreach be pull up to out of transformContainerSubscripts()? Originally transformContainerSubscripts() runs only once, but now it’s placed in a while loop, and every time this foreach needs to go through the entire indirection list, which are duplicated computation.

After revisiting the code, I think this loop of checking is_slice should be removed here.

It seems only arrsubs cares about this is_slice flag.

hstore_subs can only take a single indirection, so it can do a simple check like:

```

ai = initial_node(A_Indices, *indirection);

If (list_length(*indirection) != 1 || ai->is_slice)

{

    ereport(…)

}

```

jsonbsubs doesn’t need to check is_slice flag as well, I will explain that in my next email tougher with my new comments.

So that, “bool isSlace” can be removed from SubscriptTransform, and let every individual subs check is_slice.

(Of course, if the transform method
* does not care to support slicing, it can just throw an error if isSlice.)