How do I get millisecond precision in hive?

Question

The documentation says that timestamps support the following conversion:

•Floating point numeric types: Interpreted as UNIX timestamp in seconds with decimal precisi

Answer 1

If you want to work with milliseconds, don't use the unix timestamp functions because these consider date as seconds since epoch.

hive> describe function extended unix_timestamp;
unix_timestamp([date[, pattern]]) - Returns the UNIX timestamp
Converts the current or specified time to number of seconds since 1970-01-01.

Instead, convert the JDBC compliant timestamp to double.
E.g:

Given a tab delimited data:

cat /user/hive/ts/data.txt :
a   2013-01-01 12:00:00.423   2013-01-01 12:00:00.433
b   2013-01-01 12:00:00.423   2013-01-01 12:00:00.733

CREATE EXTERNAL TABLE ts (txt string, st Timestamp, et Timestamp) 
ROW FORMAT DELIMITED
FIELDS TERMINATED BY '\t'
LOCATION '/user/hive/ts';

Then you may query the difference between startTime(st) and endTime(et) in milliseconds as follows:

select 
  txt, 
  cast(
    round(
      cast((e-s) as double) * 1000
    ) as int
  ) latency 
from (select txt, cast(st as double) s, cast(et as double) e from ts) q;