Substraction DateTime64 from DateTime64 in SQL clickhouse BD - sql

Question

I trying to find to calculate time difference in milliseconds betweent timestamps of two tables.
like this,
SELECT value, (table1.time - table2.time) AS time_delta
but i get error :
llegal types DateTime64(9) and DateTime64(9) of arguments of function minus:
so i can't substract DateTime64 in clickhouse.
Second way i tryed use DATEDIFF , but this func is limited by "SECONDS", i need values in "MILLISECONDS"
this is supported, but i get zeros in diff, because difference is too low(few millisecond):
SELECT value, dateDiff(SECOND , table1.time, table2.platform_time) AS time_delta
this is not supported:
SELECT value, dateDiff(MILLISECOND , table1.time, table2.time) AS time_delta
What's a better way to resolve my problem?
P.S i also tryed convert values to float, it's work , but looks strange,
SELECT value, (toFloat64(table1.time) - toFloat64(table2.time)) AS time_delta
as result i get somethink like this:
value time
51167477 -0.10901069641113281

Answer 1

#ditrauth Try casting to Float64, as the subsecond portion that you are looking for is stored as a decimal. Aslo, you want DateTime64(3) for milliseconds, see the docs. see below:
CREATE TABLE dt(
start DateTime64(3, 'Asia/Istanbul'),
end DateTime64(3, 'Asia/Istanbul')
)
ENGINE = MergeTree ORDER BY end
insert into dt values (1546300800123, 1546300800125),
(1546300800123, 1546300800133)
SELECT
start,
CAST(start, 'Float64'),
end,
CAST(end, 'Float64'),
CAST(end, 'Float64') - CAST(start, 'Float64') AS diff
FROM dt
┌───────────────────start─┬─CAST(start, 'Float64')─┬─────────────────────end─┬─CAST(end, 'Float64')─┬─────────────────diff─┐
│ 2019-01-01 03:00:00.123 │ 1546300800.123 │ 2019-01-01 03:00:00.125 │ 1546300800.125 │ 0.002000093460083008 │
│ 2019-01-01 03:00:00.123 │ 1546300800.123 │ 2019-01-01 03:00:00.133 │ 1546300800.133 │ 0.009999990463256836 │
└─────────────────────────┴────────────────────────┴─────────────────────────┴──────────────────────┴──────────────────────┘
2 rows in set. Elapsed: 0.001 sec.