Hive / SparkSQL：如何将Unix时间戳转换为时间戳

Step 0: Preparation
select from_unixtime(1508673584) as fut;
Result:

-----------------------
| fut                 |
| ------------------- |
| 2017-10-22 11:59:44 |
-----------------------

Step 1: Create a table with the result of from_unixtime()

create table test
select  from_unixtime(1508673584) as fut;

Step 2: Examine the datatype of the column fut
describe test;
Result:

----------------------------------
| col_name | data_type | comment |
| -------- | --------- | ------- |
| fut      | string    | <null>  |
----------------------------------

I also tried this

select 
  from_utc_timestamp(1508618794*1000, 'EDT');

However, I got an error of

Error: org.apache.spark.sql.AnalysisException: 
  cannot resolve 'from_utc_timestamp((1508618794 * 1000), 'EDT')' 
  due to data type mismatch: 
  argument 1 requires timestamp type, 
  however, '(1508618794 * 1000)' is of int type.; line 2 pos 2;
'Project [unresolvedalias(from_utc_timestamp((1508618794 * 1000), EDT), None)]
+- OneRowRelation$

SQLState:  null
ErrorCode: 0    

解决方案
(I am providing an answer myself here.)

The answer is to use cast(). This works for both date and timestamp

select 
  from_unixtime(1508673584)                    as fut,
  cast(from_unixtime(1508673584) as date)      as futAsDate,
  cast(from_unixtime(1508673584) as timestamp) as futAsTimestamp;

Result:

------------------------------------------------------------
| fut                 | futAsDate  | futAsTimestamp        |
| ------------------- | ---------- | --------------------- |
| 2017-10-22 11:59:44 | 2017-10-22 | 2017-10-22 11:59:44.0 |
------------------------------------------------------------

Verification of data types

create table test2
select 
  from_unixtime(1508673584)                    as fut,
  cast(from_unixtime(1508673584) as date)      as futAsDate,
  cast(from_unixtime(1508673584) as timestamp) as futAsTimestamp;

And then

describe test2;
Result:

----------------------------------------
| col_name       | data_type | comment |
| -------------- | --------- | ------- |
| fut            | string    | <null>  |
| futAsDate      | date      | <null>  |
| futAsTimestamp | timestamp | <null>  |
----------------------------------------

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