Re: Row pattern recognition

> 2 - 0001 - gram.y
> ```
> opt_row_pattern_initial_or_seek:
> 			INITIAL		{ $$ = true; }
> 			| SEEK
> 				{
> 					ereport(ERROR,
> 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> 							 errmsg("SEEK is not supported"),
> 							 errhint("Use INITIAL instead."),
> 							 parser_errposition(@1)));
> 				}
> 			| /*EMPTY*/		{ $$ = true; }
> 		;
> ```
> 
> As SEEK is specially listed here, I guess it might be supported in future. If that is true, would it be better to defer the semantic check to later parse phase, which would future work easier.

From a comment in gram.y:

/*
 * If we see PARTITION, RANGE, ROWS, GROUPS, AFTER, INITIAL, SEEK or PATTERN_P
 * as the first token after the '(' of a window_specification, we want the
 * assumption to be that there is no existing_window_name; but those keywords
 * are unreserved and so could be ColIds.  We fix this by making them have the

For this purpose, we want INITIAL and SEEK to be unreserved keywords.

> 3 - 0001 - parsenodes.h
> ```
> +/*
> + * RowPatternCommonSyntax - raw representation of row pattern common syntax
> + *
> + */
> +typedef struct RPCommonSyntax
> +{
> +	NodeTag		type;
> +	RPSkipTo	rpSkipTo;		/* Row Pattern AFTER MATCH SKIP type */
> +	bool		initial;		/* true if <row pattern initial or seek> is
> +								 * initial */
> +	List	   *rpPatterns;		/* PATTERN variables (list of A_Expr) */
> +	List	   *rpDefs;			/* row pattern definitions clause (list of
> +								 * ResTarget) */
> +} RPCommonSyntax;
> +
>  /*
>   * WindowDef - raw representation of WINDOW and OVER clauses
>   *
> @@ -593,6 +618,7 @@ typedef struct WindowDef
>  	char	   *refname;		/* referenced window name, if any */
>  	List	   *partitionClause;	/* PARTITION BY expression list */
>  	List	   *orderClause;	/* ORDER BY (list of SortBy) */
> +	RPCommonSyntax *rpCommonSyntax; /* row pattern common syntax */
> ```
> 
> RP fields are directly defined in WindowClause, then why do we need a wrapper of RPCommonSyntax? Can we directly define RP fields in WindowRef as well?

The row pattern common syntax defined in the standard is not only used
in the WINDOW clause, but in the FROM clause. If we would support RPR
in FROM clause in the future, it would be better to use the same code
of row pattern common syntax in WINDOW clause as much as
possible. That's the reason I created RPCommonSyntax. In the
parse/analysis phase, I am not sure how the parse/analysis code would
be in FROM clause at this point. So I did not define yet another
struct for it.

Best regards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp