(Primary Key: One or more fields (columns) whose values uniquely identify each record in a table. A primary key cannot allow Null values and must always have a unique index. A primary key is used to relate a table to foreign keys in other tables.)

What is needed to uniquely identify a record in a database?

PRIMARY KEY in DBMS is a column or group of columns in a table that uniquely identify every row in that table. The Primary Key can't be a duplicate meaning the same value can't appear more than once in the table. A table cannot have more than one primary key.

How does columnar database store data?

A columnar database stores data by columns rather than by rows, which makes it suitable for analytical query processing, and thus for data warehouses. ... Data warehouses benefit from the higher performance they can gain from a database that stores data by column rather than by row.