There are two types of views: simple and complex. Table 10.2 compares the two types of views.
Simple views can be used in DML statements because the records displayed in a simple view relate to one row of a table. Complex-view records are virtual records and do not generally relate to one row of a table. The DELETE command cannot be used against a complex view if the view has any of the following features:
Contains a group function
Contains a GROUP BY clause
Contains the DISTINCT keyword
Contains the pseudocolumn ROWNUM
A view cannot be updated if the view contains any of the above properties. It also cannot be updated if the view has the following property:
Contains a column that is defined by expressions. These are columns that ...