How to convert epoch to datetime redshift? - datetime

Question

I work in dbeaver. I have a table x.
TABLE x has a column "timestamp"
1464800406459
1464800400452
1464800414056
1464800422854
1464800411797
The result I want:
Wed, 01 Jun 2016 17:00:06.459 GMT
Wed, 01 Jun 2016 17:00:00.452 GMT
Wed, 01 Jun 2016 17:00:14.056 GMT
Wed, 01 Jun 2016 17:00:22.854 GMT
Wed, 01 Jun 2016 17:00:11.797 GMT
I tried redshift query
SELECT FROM_UNIXTIME(x.timestamp) as x_date_time
FROM x
but didn't work.
Error occurred:
Invalid operation: function from_unixtime(character varying) does not exist
I also tried
SELECT DATE_FORMAT(x.timestamp, '%d/%m/%Y') as x_date
FROM x
Error occurred:
Invalid operation: function date_format(character varying, "unknown") does not exist
Is there any wrong with the syntax? Or is there another way to convert to human readable date and time?

Answer 1

Redshift doesn't have the from_unixtime() function. You'll need to use the below SQL query to get the timestamp. It just adds the number of seconds to epoch and return as timestamp.
select timestamp 'epoch' + your_timestamp_column * interval '1 second' AS your_column_alias
from your_table

Answer 2

UDF is going to be pretty slow. Checked execution time for 3 solutions and 1k rows.
The slowest -
-- using UDF from one of the answers
SELECT from_unixtime(column_with_time_in_ms/ 1000)
FROM table_name LIMIT 1000;
Execution time: 00:00:02.348062s
2nd best -
SELECT date_add('ms',column_with_time_in_ms,'1970-01-01')
FROM table_name LIMIT 1000;
Execution time: 00:00:01.112831s
And the fastest -
SELECT TIMESTAMP 'epoch' + column_with_time_in_ms/1000 *INTERVAL '1 second'
FROM table_name LIMIT 1000;
Execution time: 00:00:00.095102s
Execution time calculated from stl_query -
SELECT *
,endtime - starttime
FROM stl_query
WHERE querytxt ilike('%table_name%limit%')
ORDER BY starttime DESC;

Answer 3

The simplest solution is to create from_unixtime() function:
CREATE OR REPLACE FUNCTION from_unixtime(epoch BIGINT)
RETURNS TIMESTAMP AS
'import datetime
return datetime.datetime.fromtimestamp(epoch)
'
LANGUAGE plpythonu IMMUTABLE;
See Redshift documentation on UDF for details

Answer 4

For quick reference, here is the SQL UDF implementation of the from_unixtime function shown above in Python. I've not tested the performance but I imagine it would be similar to the plain SQL version. It's a whole lot easier to write though.
Note: this calculates the number of seconds from the epoch.
CREATE FUNCTION from_unixtime (BIGINT)
  RETURNS TIMESTAMP WITHOUT TIME ZONE
IMMUTABLE
as $$
  SELECT TIMESTAMP 'epoch' + $1 / 1000 * interval '1 second'
$$ LANGUAGE sql;

Answer 5

I used it like this
CAST(DATEADD(S, CONVERT(int,LEFT(column_name, 10)), '1970-01-01')as timestamp) as column_name
SELECT
,task_id
,CAST(DATEADD(S, CONVERT(int,LEFT(SLA, 10)), '1970-01-01')as timestamp) as SLA
FROM my_schema.my_task_table ;