Hi,
Flink relational apis with MATCH_RECOGNITION looks very attractive and promising but it's currently not easy to use at all.
While looking into [1],
especially the following DEFINE clause,
DEFINE
PRICE_DOWN AS
(LAST(PRICE_DOWN.price, 1) IS NULL AND PRICE_DOWN.price < START_ROW.price) OR PRICE_DOWN.price < LAST(PRICE_DOWN.price, 1),
PRICE_UP AS
PRICE_UP.price > LAST(PRICE_DOWN.price, 1)
what came up to my mind is that the condition is quite verbose.
Meanwhile, I found [2] in which Oracle uses the similar data and the MATCH_RECOGNIZE clause as follows:
SELECT *
FROM Ticker MATCH_RECOGNIZE (
PARTITION BY symbol
ORDER BY tstamp
MEASURES STRT.tstamp AS start_tstamp,
LAST(DOWN.tstamp) AS bottom_tstamp,
LAST(UP.tstamp) AS end_tstamp
ONE ROW PER MATCH
AFTER MATCH SKIP TO LAST UP
PATTERN (STRT DOWN+ UP+)
DEFINE
DOWN AS DOWN.price < PREV(DOWN.price),
UP AS UP.price > PREV(UP.price)
) MR
ORDER BY MR.symbol, MR.start_tstamp;
Oracle's way of defining pattern variables looks much simple and neat thanks to
1) its use of PREV which is not available in Flink's MATCH_RECOGNIZE clause (mentioned in [3])
2) no need to check the initial case or when there is no last row that met the PRICE_DOWN condition
Is there a way to shorten the DEFINE cluase in MATCH_RECOGNIZE at Flink 1.8 or 1.9?
If there's any plan regarding this, could anyone let me know related Jira issues?
Best,
Dongwon
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