how to convert unix epoch time to date string in hive

If you need to convert the date in custom format, use this:

select date_format(from_unixtime(epoch_datetime),'yyyyMM') as formatted_date from myHiveTable;

which will return the date as yearMonth e.g. 201708

Oof, that looks ugly. Try using this function in Hive:

SELECT from_unixtime(unix_timestamp) as new_timestamp from raw_data ...

Or if timestamp is in ms instead of seconds:

SELECT from_unixtime(unix_timestamp DIV 1000) as new_timestamp from raw_data ...

That converts a unix timestamp into a YYYY-MM-DD HH:MM:SS format, then you can use the following functions to get the year, month, and day:

SELECT year(new_timestamp) as year, month(new_timestamp) as month, day(new_timestamp) as day ...

With more recent releases of Hive and SparkSQL, data type of date and type casting options are available. Following should work in Hive as well as Spark SQL

SELECT cast(from_unixtime(epoch_datetime) as date) from myHiveTable