Feedback-ID: ia2694551:Fastmail
Date: Tue, 21 Mar 2023 11:28:49 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Vik Fearing <vik@postgresfriends.org>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: MERGE ... WHEN NOT MATCHED BY SOURCE
Message-ID: <20230321102849.ajmumhbngak3ltkw@alvherre.pgsql>
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On 2023-Mar-19, Dean Rasheed wrote:

> diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
> new file mode 100644
> index efe88cc..e1ebc8d
> --- a/src/backend/parser/gram.y
> +++ b/src/backend/parser/gram.y

> +merge_when_tgt_matched:
> +			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
> +			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
> +		;

I think a one-line comment on why this "matched" production matches "NOT
MATCHED BY" would be useful.  I think you have a big one in
transformMergeStmt already.


> +			/* Combine it with the action's WHEN condition */
> +			if (action->qual == NULL)
> +				action->qual = (Node *) ntest;
> +			else
> +				action->qual =
> +					(Node *) makeBoolExpr(AND_EXPR,
> +										  list_make2(ntest, action->qual),
> +										  -1);

Hmm, I think ->qual is already in implicit-and form, so do you really
need to makeBoolExpr, or would it be sufficient to append this new
condition to the list?

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"El miedo atento y previsor es la madre de la seguridad" (E. Burke)