flinksql里面最常用的事情就是时间格式转换，比如各种时间格式转换成TIMESTAMP(3).
now() bigint-- CAST(TO_TIMESTAMP(log_time) as TIMESTAMP(3)) ,log_time=now()
localtimestamp timestamp(3)
timestamp – 不带括号数字表示timestamp(6)
now() 1403006911000 bigint – 毫秒时间戳数值
localtimestamp 1636272032500 timestamp(3) – 毫秒时间戳
timestamp(3) 1636272032500 – 毫秒时间戳
timestamp(9)
timestamp(6)
TIMESTAMP(9) TO_TIMESTAMP(BIGINT time)
TIMESTAMP(9) TO_TIMESTAMP(STRING time)
TIMESTAMP(9) TO_TIMESTAMP(STRING time, STRING format)
BIGINT TIMESTAMP_TO_MS(TIMTSTAMP time)
BIGINT TIMESTAMP_TO_MS(STRING time, STRING format)
TO_DATE(CAST(LOCALTIMESTAMP AS VARCHAR))
FROM_UNIXTIME(TIMESTAMP_TO_MS(localtimestamp)/1000, ‘yyyy-MM-dd HH:mm:ss’)
参考文档：
https://ci.apache.org/projects/flink/flink-docs-master/zh/docs/dev/table/concepts/timezone/
