Re: Row pattern recognition

> On 18/11/2025 06:03, Chao Li wrote:
>> 1 - 0001 - kwlist.h
>> ```
>> +PG_KEYWORD("define", DEFINE, RESERVED_KEYWORD, BARE_LABEL)
>> ```
>>
>> Why do we add “define” as a reserved keyword? From the SQL example
>> you put in 0006:
>> ```
>> <programlisting>
>> SELECT company, tdate, price,
>> first_value(price) OVER w,
>> max(price) OVER w,
>> count(price) OVER w
>> FROM stock
>> WINDOW w AS (
>> PARTITION BY company
>> ORDER BY tdate
>> ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
>> AFTER MATCH SKIP PAST LAST ROW
>> INITIAL
>> PATTERN (LOWPRICE UP+ DOWN+)
>> DEFINE
>> LOWPRICE AS price &lt;= 100,
>> UP AS price &gt; PREV(price),
>> DOWN AS price &lt; PREV(price)
>> );
>> </programlisting>
>> ```
>>
>> PARTITION is at the same level as DEFINE, but it’s not defined as a
>> reserved keyword:
>> ```
>> PG_KEYWORD("partition", PARTITION, UNRESERVED_KEYWORD, BARE_LABEL)
>> ```
>>
>> Even in this patch,”initial”,”past”, “pattern” and “seek” are
>> defined as unreserved, why?
>>
>> So I just want to clarify.
>
>
> Because of position. Without making DEFINE a reserved keyword, how do
> you know that it isn't another variable in the PATTERN clause?

I think we don't need to worry about this because PATTERN_P is in the
$nonassoc list in the patch, which gives PATTERN different precedence
from DEFINE.

@@ -888,6 +896,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
%nonassoc UNBOUNDED NESTED /* ideally would have same precedence as IDENT */
%nonassoc IDENT PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
SET KEYS OBJECT_P SCALAR VALUE_P WITH WITHOUT PATH
+ AFTER INITIAL SEEK PATTERN_P

And I think we could change DEFINE to an unreserved keyword. Attached
is a patch to do that, on top of v35-0001.

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