Java 如何在sparksql中获得今天-“1天”日期？
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How to get today -"1 day" date in sparksql?
提问by Vishan Rana
How to get current_date - 1day in sparksql, same as cur_date()-1in mysql.
如何current_date - 1在 sparksql 中获取日期，与cur_date()-1在 mysql 中相同。
采纳答案by Ram Ghadiyaram
The arithmetic functions allow you to perform arithmetic operation on columns containing dates.
算术函数允许您对包含日期的列执行算术运算。
For example, you can calculate the difference between two dates, add days to a date, or subtract days from a date. The built-in date arithmetic functions include datediff, date_add, date_sub, add_months, last_day,
next_day, and months_between.
例如，您可以计算两个日期之间的差值、向日期添加天数或从日期中减去天数。内置的日期计算功能包括datediff，date_add，date_sub，add_months，last_day，
next_day，和months_between。
Out of above what we need is
除了上面我们需要的是
date_sub(timestamp startdate, int days), Purpose: Subtracts a specified number of days from a TIMESTAMP value. The first argument can be a string, which is automatically cast to TIMESTAMP if it uses the recognized format, as described in TIMESTAMP Data Type. Return type: Returns the date that is > days days before start
date_sub(timestamp startdate, int days), 目的：从 TIMESTAMP 值中减去指定的天数。第一个参数可以是一个字符串，如果它使用可识别的格式，它会自动转换为 TIMESTAMP，如 TIMESTAMP 数据类型中所述。返回类型：返回开始前 > 天的日期
and we have
我们有
current_timestamp() Purpose: Alias for the now() function. Return type: timestamp
current_timestamp() 目的： now() 函数的别名。返回类型：时间戳
you can do select
你可以选择
date_sub(CAST(current_timestamp() as DATE), 1)
See https://spark.apache.org/docs/1.6.2/api/java/org/apache/spark/sql/functions.html
见https://spark.apache.org/docs/1.6.2/api/java/org/apache/spark/sql/functions.html
回答by Shiv4nsh
You can easily perform this task , there are many methods related to the date and what you can use here is date_sub
您可以轻松地执行此任务，有许多与日期相关的方法，您可以在这里使用的是 date_sub
Example on Spark-REPL:
Spark-REPL 示例：
scala> spark.sql("select date_sub(current_timestamp(), 1)").show
+----------------------------------------------+
|date_sub(CAST(current_timestamp() AS DATE), 1)|
+----------------------------------------------+
| 2016-12-12|
+----------------------------------------------+
回答by TAYFUN CANAKCI
回答by Kai
Yes, the date_sub()function is the right for the question, anyway, there's an error in the selected answer:
是的，该date_sub()函数适合该问题，无论如何，所选答案中存在错误：
Return type: timestamp
返回类型：时间戳
The return type should be dateinstead, date_sub() function will trim any hh:mm:sspart of the timestamp, and returns only a date.
返回类型应该是date， date_sub() 函数将修剪hh:mm:ss时间戳的任何部分，并且只返回一个date.
