Spark3.0中Dates和Timestamps

Spark3.0使用的是预公历，而之前都是儒略历和公历的混合（即1582年之前的日期使用儒略历，1582年之后使用公历，java.sql.Date这个API用的就是这种，而Java8里使用java.time.LocalDate代替，使用的就是Spark3.0目前的预公历），Date类型不考虑时区

Spark3.0移植了Java8中的时间戳，将更加精确

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构造日期和时间戳

1、构造日期

• 　　make_date(),spark3.0中该函数有三个参数：YEAR，MONTH，DAY，输入参数均被隐式转换为int类型，该函数会根据预公历检查形成的日期是否是有效日期，无效则返回NULL。

• >>> spark.createDataFrame([(2020, 6, 26), (1000, 2, 29), (-44, 1, 1)],
  ... ['Y', 'M', 'D']).createTempView('YMD')
  >>> df = sql('select make_date(Y, M, D) as date from YMD')
  >>> df.printSchema()
  root
   |-- date: date (nullable = true)
  >>> df.show()
  +-----------+
  |       date|
  +-----------+
  | 2020-06-26|
  |       null|
  |-0044-01-01|
  +-----------+    

2、构造时间戳

• 　　make_timestamp(),  spark3.0中共有6个参数，YEAR，MONTH，DAY，HOUR，MINUTE，SECOND，其中second为decimal类型，因为时间戳中的秒可以以微秒形式传递，提高精度

• >>> df = spark.createDataFrame([(2020, 6, 28, 10, 31, 30.123456),
  ... (1582, 10, 10, 0, 1, 2.0001), (2019, 2, 29, 9, 29, 1.0)],
  ... ['YEAR', 'MONTH', 'DAY', 'HOUR', 'MINUTE', 'SECOND'])
  >>> df.show()
  +----+-----+---+----+------+---------+
  |YEAR|MONTH|DAY|HOUR|MINUTE|   SECOND|
  +----+-----+---+----+------+---------+
  |2020|    6| 28|  10|    31|30.123456|
  |1582|   10| 10|   0|     1|   2.0001|
  |2019|    2| 29|   9|    29|      1.0|
  +----+-----+---+----+------+---------+
  
  >>> ts = df.selectExpr("make_timestamp(YEAR, MONTH, DAY, HOUR, MINUTE, SECOND) as MAKE_TIMESTAMP")
  >>> ts.printSchema()
  root
   |-- MAKE_TIMESTAMP: timestamp (nullable = true)
  >>> ts.show(truncate=False)
  +--------------------------+
  |MAKE_TIMESTAMP            |
  +--------------------------+
  |2020-06-28 10:31:30.123456|
  |1582-10-10 00:01:02.0001  |
  |null                      |
  +--------------------------+
  //转换时区只需要再加一个参数，如下

  >>> df = spark.createDataFrame([(2020, 6, 28, 10, 31, 30, 'UTC'),
  ...     (1582, 10, 10, 0, 1, 2, 'America/Los_Angeles'),
  ...     (2019, 2, 28, 9, 29, 1, 'Europe/Moscow')],
  ...     ['YEAR', 'MONTH', 'DAY', 'HOUR', 'MINUTE', 'SECOND', 'TZ'])
  >>> df = df.selectExpr('make_timestamp(YEAR, MONTH, DAY, HOUR, MINUTE, SECOND, TZ) as MAKE_TIMESTAMP')
  >>> df = df.selectExpr("date_format(MAKE_TIMESTAMP, 'yyyy-MM-dd HH:mm:SS VV') AS TIMESTAMP_STRING")
  >>> df.show(truncate=False)
  +---------------------------------+
  |TIMESTAMP_STRING                 |
  +---------------------------------+
  |2020-06-28 13:31:00 Europe/Moscow|
  |1582-10-10 10:24:00 Europe/Moscow|
  |2019-02-28 09:29:00 Europe/Moscow|
  +---------------------------------+