TTL设置

最佳实践：显示要用请配置State TTL Config，在精确性和大小之间的权衡。

streamQueryConfig.withIdleStateRetentionTime(Time.day(1), Time.day(2))

Group Windows

TUMBLE(t, INTERVAL '2' HOUR)
HOP(t, INTERVAL '2' HOUR, INTERVAL '1' HOUR)
SESSION(t, INTERVAL '30' MINUTE)

SELECT user, TUMBLE_END(ctime, INTERVAL '1' HOURS) AS end_time, COUNT(url) AS cnt
FROM click GROUP BY user TUMBLE(ctime, INTERVAL '1' HOURS);

Group Aggregation

每来一条都更新一次结果。后面最好接幂等Sink，MySQL和HBase这类。要不然会出现一大堆历史数据（可能根本不需要）。

SELECT user, COUNT(url) as cnt FROM click GROUP BY user;

INSERT INTO sink
SELECT * FROM source;

Over Window

https://help.aliyun.com/document_detail/62514.html?spm=a2c4g.11186623.6.765.613260bcR4TzE4

SQL 子句优先级