An index stores both the values of a table's columns and a system of directions that enable access to rows in that table by index value. Defining an index on a column or set of columns enables SAS, ...

SQL Server 2014 introduces clustered columnstore indexes, which become the primary storage method for the table. These can be updated, but cannot be combined with any other indexes.

Duplicate and Ignore on MySQL Inserts. MySQL table primary keys and unique indexes prevent multiple rows with the same index from being added to the table. If you try to insert a duplicate row ...