July 10, 2016

Difference between view and Materialized view and Define Long Column

Difference between view and Materialized view 

(i) View will not store any data,whereas Materialized View will store data.
(ii)View is used for security purpose and Materialized View for performance.
(iii) view is not accessible if base table is dropped, whereas in Materialized View it can still be accessible.
(iv) Can perform DML operation directly on view but it Materialized View its not possible.

Define Long Column

LONG columns cannot be in the SELECT clause when using the UNION set operators. There are some restrictions for long columns like. 
(i) It cannot appear in where clause.
(ii) Indexes cannot be created on them.
(iii) It cannot appear in Group by,order by, or connect by clauses or with the distinct operator in select statements.