[Bug fix] Divide by 1000.000 in epoch_ms_to_dttm() to not lose precision in Presto

[ghost]

Context:

presto> SELECT CAST(from_unixtime((1528761599980/1000.0)) AS TIMESTAMP);
-------------------------
 2018-06-12 00:00:00.000

presto> SELECT CAST(from_unixtime((1528761599980/1000)) AS TIMESTAMP);
-------------------------
 2018-06-11 23:59:59.000

presto> SELECT CAST(from_unixtime((1528761599980/1000.00)) AS TIMESTAMP);
-------------------------
 2018-06-11 23:59:59.980

In an unfortunate event where the entry is < 1 second from the next day, the generated query casts it to the next day. This shouldn't be a problem in MySQL, but it is in Presto.

[john-bodley]

@evelynturner I'm not sure this is necessary given that dividing an integer by a float returns a float, i.e.,

presto:default> SELECT CAST(from_unixtime((1528761599980/1000.0)) AS TIMESTAMP);
 2018-06-11 23:59:59.980 

works as expected.

[ghost]

@john-bodley That's because of your parse_decimal_literals_as_double setting..

For compatibility reasons decimal literals without explicit type specifier (e.g. 1.2) are treated as the values of the DOUBLE type by default, but this is subject to change in future releases. This behavior is controlled by:
System wide property: parse-decimal-literals-as-double
Session wide property: parse_decimal_literals_as_double

https://prestodb.io/docs/current/language/types.html#floating-point

I can always set it as true, but I didn't see any harm in accommodating to the other setting as well. Maybe we can document it somewhere that people need to set those properties as true for Presto then.

[mistercrunch]

LGTM though can you rebase?

[codecov-io]

Codecov Report

Merging #5211 into master will decrease coverage by 16.15%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #5211       +/-   ##
===========================================
- Coverage   77.48%   61.32%   -16.16%     
===========================================
  Files          44      369      +325     
  Lines        8749    23488    +14739     
  Branches        0     2717     +2717     
===========================================
+ Hits         6779    14405     +7626     
- Misses       1970     9071     +7101     
- Partials        0       12       +12

Impacted Files	Coverage Δ
superset/db_engine_specs.py	54.28% <ø> (+0.56%)	⬆️
superset/sql_lab.py	71.6% <0%> (-3.81%)	⬇️
superset/dataframe.py	94.49% <0%> (-3.21%)	⬇️
superset/views/core.py	72.96% <0%> (-1.71%)	⬇️
superset/models/core.py	85.29% <0%> (-1.26%)	⬇️
superset/__init__.py	72.32% <0%> (-0.79%)	⬇️
superset/utils.py	87.8% <0%> (-0.72%)	⬇️
superset/exceptions.py	100% <0%> (ø)	⬆️
superset/connectors/druid/models.py	80.56% <0%> (ø)	⬆️
...sets/src/explore/components/DisplayQueryButton.jsx	84.21% <0%> (ø)
... and 328 more

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