Re:HyPer – A Hybrid OLTP and OLAP High-Performance DBMS
by makmanalp on Wednesday January 14, 2015 @03:42PM
(#8888878)
At first I thought you could do this with window functions (http://www.postgresql.org/docs/9.1/static/tutorial-window.ht...) but now I'm not so sure, or at least it doesn't seem very straightforward to me - very neat!
And that's a good thing.
You can use sql to query it if you want by starting the query with "s)" in the console, or simply by using the ODBC/JDBC drivers.
But KDB+ embraces order in a way that SQL does not, which means that if you limit yourself to SQL then you miss out on a lot power that KDB gives you.
For example, say you want to select a list of (date,teacher) records ordered by date, and out of these pick out the records in which the teacher is not the same as in the previous date.
In kdb+, it's "select from (select from records by date) where differ teacher" (or just "&~=':teacher[<date]" if you use K notation). What's the SQL equivalent?