I heard that there is a difference when you query (select, etc.) from HDB and RDB (in-memory) databases. Is it possible to describe all possible scenarios when we should use HDB specific queries and RDB specific queries and how to query: i.e. example of the query for HDB and the same example for RDB?
Off the top of my head:
Partitioned HDB tables will have a "virtual" date column
RDB tables (generally) won't have a `date column
The virtual "i" column behaves differently for Partitioed HDB tables (http://code.kx.com/q/ref/dotq/#qind-partitioned-index)
HDB tables (unless stored flat/serialised) are not immediately pulled entirely into memory, data is read on demand
The symbol columns in HDB tables will be enumerated, in-memory RDB tables will be unenumerated
There's no real examples I can give but you just need to keep these in mind when querying