How do I convert Bigint to Timestamp with Presto?

UNIX timestamps are normally stored as doubles. If you have UNIX timestamps stored as big integers then you may encounter errors when trying to cast them as timestamps:

presto> select col1 from table_a;
presto> select cast(col1 as timestamp) from table_a;
Query 20201127_150824_00052_xnxra failed: line 1:8: Cannot cast bigint to timestamp

There is a solution!  Presto’s from_unixtime() function takes a UNIX timestamp and returns a timestamp:

presto> select col1,from_unixtime(col1) as ts from table_a;
    col1    |          ts          
 1606485526 | 2020-11-27 13:58:46.000 
 1606485575 | 2020-11-27 13:59:35.000 

And we can optionally modify the format of the result by using date_format():

presto> select date_format(from_unixtime(col1),'%Y-%m-%d %h:%i%p') from table_a;
 2020-11-27 01:58PM 
 2020-11-27 01:59PM 

That’s how to use from_unixtime() to convert a bigint to timestamp.