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From: Chao Li <[email protected]>
To: Alexandra Wang <[email protected]>
Cc: jian he <[email protected]>
Cc: Nikita Malakhov <[email protected]>
Cc: Vik Fearing <[email protected]>
Cc: Mark Dilger <[email protected]>
Cc: Matheus Alcantara <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Nikita Glukhov <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: David E. Wheeler <[email protected]>
Subject: Re: SQL:2023 JSON simplified accessor support
Date: Tue, 2 Sep 2025 10:59:39 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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> On Aug 29, 2025, at 15:22, Chao Li <[email protected]> wrote:
> 
> +static bool
> +jsonb_check_jsonpath_needed(List *indirection)
> +{
> +       ListCell   *lc;
> +
> +       foreach(lc, indirection)
> +       {
> +               Node       *accessor = lfirst(lc);
> +
> +               if (IsA(accessor, String))
> +                       return true;
> 
> Like I mentioned in my previous comment, if we convert String (dot notation) to Indices in rewritten phase, then jsonpath might be no longer needed, and the code logic is much simplified.
> 

Taking back this comment. As Alex explained in the other email, dot notation and indices accessor are different.

> 
> --- 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.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/





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