Prerequisite – SQL | Views
A View in SQL as a logical subset of data from one or more tables. Views are used to restrict data access. A View contains no data of its own but its like window through which data from tables can be viewed or changed. The table on which a View is based are called BASE Tables.
There are 2 types of Views in SQL: Simple View and Complex View. Simple views can only contain a single base table. Complex views can be constructed on more than one base table. In particular, complex views can contain: join conditions, a group by clause, a order by clause.
The key differences between these types of Views are:
Simple View | Complex View |
---|---|
Contains only one single base table or is created from only one table. | Conatins more than one base tables or is created from more than one tables. |
We cannot use group functions like MAX(), COUNT(), etc. | We can use group functions. |
Does not contain groups of data. | It can conatin groups of data. |
DML operations could be performed through a simple view. | DML operations could not always be performed through a complex view. |
INSERT, DELETE and UPDATE are directly possible on a simle view. | We cannot apply INSERT, DELETE and UPDATE on complex view directly. |
Simple view does not contain group by, distinct, pseudocolumn like rownum, columns defiend by expressions. | It can contain group by, distinct, pseudocolumn like rownum, columns defiend by expressions. |
Does not include NOT NULL columns from base tables. | NOT NULL columns that are not selected by simple view can be included in complex view. |
Reference –
View – orafaq
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