Row oriented vs column oriented databases
SELECT correlation(feature2, feature5) FROM records
-- we just have to read the columns which are interested in
-- allows better compression, since the data in one specific column is homogeneous than across all the columns.
-- but: manipulating (lookup, update or delete) an entire given row is inefficient, which occur rarely in databases for analytics
-- ref: https://datascience.stackexchange.com/questions/8244/what-makes-columnar-databases-suitable-for-data-science