string to date - hive SQL - sql

Question

I am running queries in a hive environment.
I have a column which has a timestamp but is set up a string in the tables. I tried the following : all of them return Null
SELECT
,To_date(activitydate)
Cast:
,cast(activitydate as timestamp)
This is the how the data is set up in the table:
Appreciate any inputs on how I can convert this :
05/12/2017 00:00:00
SELECT
cust_id
,to_date(activitydate) activity_date
,type type_of_contact
FROM repl_task
WHERE to_date(activitydate) BETWEEN '2014-01-01' AND '2017-01-01' ;
I am running out of memory if I run this :
SELECT
cust_id
,activitydate
,SUBSTR(activitydate,4,2) AS DT
,SUBSTR(activitydate,0,2) AS MONTH
,SUBSTR(activitydate,7,4) AS YEAR
,type
FROM task
WHERE activitydate >='01/01/2016 00:00:00'

Answer 1

unix_timestamp function converts given format to unix timestamp and from_unixtime function converts from unix timestamp to given format:
hive> select from_unixtime(unix_timestamp('01/01/2016 00:00:00','MM/dd/yyyy HH:m:ss'),'yyyy-MM-dd');
OK
2016-01-01
Time taken: 0.118 seconds, Fetched: 1 row(s)

Answer 2

Can you try using to_date() with the date portion of your timestamp in ISO format:
SELECT
cust_id,
TO_DATE(CONCAT(SUBSTR(activitydate, 7, 4), '-',
SUBSTR(activitydate, 0, 2), '-',
SUBSTR(activitydate, 4, 2))) activity_date
type type_of_contact
FROM repl_task
WHERE
TO_DATE(CONCAT(SUBSTR(activitydate, 7, 4), '-',
SUBSTR(activitydate, 0, 2), '-',
SUBSTR(activitydate, 4, 2)))
BETWEEN '2014-01-01' AND '2017-01-01';
If this runs, but is not very performant, then you should consider storing your timestamps in ISO format. Storing dates as text, or as text in a non standard format, carries a penalty with most databases.