如何将可空列中的时间戳转换为 aws athena 中的日期？

Question

I want to convert datatype of string (eg: '2018-03-27T00:20:00.855556Z' ) into date (eg: '2018-03-27')

problem is cast(substring(dt, 1, 10) as date) doesn't work here (INVALID_CAST_ARGUMENT: Value cannot be cast to date) and the column has null values and empty strings so from_iso8601_timestamp will fail (INVALID_FUNCTION_ARGUMENT: Invalid format: "")

Answer 1

problem is cast(substring(dt, 1, 10) as date) doesn't work here

Was not able to reproduce, works just fine for me -

select cast(substring('2018-03-27T00:20:00.855556Z', 1, 10) as date);

Output:

_col0
2018-03-27

The problem seems to be the same as for from_iso8601_timestamp - empty strings, so you can usetry (swallows all exceptions and returns null):

select try(from_iso8601_timestamp(dt)) dt
from (values ('2018-03-27T00:20:00.855556Z'),(null), ('')) as t(dt);

or check if string is empty:

select from_iso8601_timestamp(if(dt = '', null, dt)) dt
from (values ('2018-03-27T00:20:00.855556Z'),(null), ('')) as t(dt);

Output:

dt
2018-03-27 00:20:00.855 UTC
NULL
NULL