Support supplying raw integers in DateTime columns to avoid costly ti…

[wawaka]

Ability to use integer for datetime columns allows to dramatically improve performance of INSERT operations with a lots of DateTime values (about 4x times)

[coveralls]

Coverage increased (+0.004%) to 95.566% when pulling 46a29a1 on wawaka:datetime_support_int into 5928ee3 on mymarilyn:master.

[coveralls]

Coverage increased (+0.6%) to 96.211% when pulling 9a5ca36 on wawaka:datetime_support_int into 5928ee3 on mymarilyn:master.

[xzkostyan]

Hi.

Great. There is overhead on datetime to int conversion. Does clickhouse-client allow raw integer insert into DatetTme field? If yes, this is really useful feature.

What about Date field? Integer also can be passed to it.

Tests are required for any new features. There are lots of examples in tests package.

[wawaka]

Yes, clickhouse-client supports parsing DateTime values from integers timestamps.

For Date field - I believe it's much less common to pass Date value as an integer.
And it does not have such performance penalty to convert date to number of days as opposed to datetime and it's manipulations with timezones.

[xzkostyan]

Great, but let's insert whole values in one insert: 'INSERT INTO test (a) VALUES', [(0, ), (1, ), (1500000000, ), (2**32-1, )]. It will be a little more readable.