Example: Unix time
Unix time (also known as POSIX time or UNIX Epoch time) is a system for describing a point in time as the number of seconds that have elapsed since 00:00:00 Thursday, 1 January 1970, Coordinated Universal Time (UTC), minus leap seconds.
If your data includes representation of Unix time as an integer, or you require converting to it, the following functions are available:
let fromUnixTime = (t:long)
{
datetime(1970-01-01) + t * 1sec
};
print result = fromUnixTime(1546897531)
let toUnixTime = (dt:datetime)
{
(dt - datetime(1970-01-01)) / 1s
};
print result = toUnixTime(datetime(2019-01-07 21:45:31.0000000))
from : https://docs.microsoft.com/en-us/azure/data-explorer/kusto/query/datetime-timespan-arithmetic