Support non timestamp type time field

[peter146d]

It's realy a great work, but unfortunately i had a legacy cassandra table that use "bigint" as the only "Time Column" and it seemed the "Time Column" only support "timestamp" type.

It would be great if it can support "$__unixEpochFrom" and "$__unixEpochFrom" such as other database data source.

Thank You.

[cnoelle]

A workaround could be to use blobAsTimestamp(bigintAsBlob(someColumn)). See https://docs.datastax.com/en/cql-oss/3.3/cql/cql_reference/blob_r.html.

[HadesArchitect]

@unflag This one is closed by #172, is it?

[unflag]

Not exactly, unfortunately. There are two problems:

• Support $__unixEpochFrom/$__unixEpochTo macros to use their values in query, which should be easy to implement.
• Convert returned bigint value to timestamp, because without this grafana will consider it a value, not a time. And there is a question - how to decide which numeric value in a row is a timestamp and which is a numeric value? I guess, we should rely on cassandra functions and convert types in query, not in datasource.

[HadesArchitect]

Theoretically we can decide based on the argument's order, can we?