获取cassandra cql select中的当前日期 [英] Get current date in cassandra cql select

问题描述

在SQL中，我能够做到：

In SQL, I am able to do:

select getdate(), getdate() - 7

返回当前日期以及当前日期-7天。我想在Cassandra CQL中实现相同的目的。我试过了：

Which returns the current date as well as current date - 7 days. I want to achieve the same in Cassandra CQL. I tried:

select dateof(now())

但这不起作用。它仅适用于插入，不适用于选择。我怎么能得到相同的？

But that does not work. It works only on insert and not in select. How can I get the same? Any help would be appreciated.

推荐答案

select dateof(now())

单靠正确，这是行不通的。但是，如果您有一个只知道一行的表（例如 system.local ）：

On its own, you are correct, that does not work. But if you have a table that you know only has one row (like system.local):

aploetz@cqlsh:stackoverflow> SELECT dateof(now()) FROM system.local ;

 dateof(now())
--------------------------
 2015-03-26 03:18:39-0500

(1 rows)

很遗憾，Cassandra CQL不提供支持（ CASSANDRA-5505 ）不包含支持对于算术运算，更不用说日期算术了。因此，从该值中减去7天是您在应用程序级别中必须要做的事情。

Unfortunately, Cassandra CQL does not (yet? CASSANDRA-5505) include support for arithmetic operations, let alone date arithmetic. So subtracting 7 days from that value is something that you would have to do in your application level.

编辑20200422

较新的语法使用 toTimestamp（）函数代替：

The newer syntax uses the toTimestamp() function instead:

aploetz@cqlsh> SELECT toTimestamp(now()) FROM system.local;

 system.totimestamp(system.now())
----------------------------------
  2020-04-22 13:22:04.752000+0000

(1 rows)

这两种语法在20200422之前都有效。

Both syntaxes work as of 20200422.

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