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Views in Database - Creating, Modifying, and Retrieving Data

This chapter focuses on creating, modifying, and retrieving data from views in a database, including advantages, creating views, checking structure and content, using column aliases and functions, modifying views, and creating views from multiple tables.

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Views in Database - Creating, Modifying, and Retrieving Data

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  1. Chapter 2 Views

  2. Objectives • Create views • Modify/Drop Views • Insert/Delete/Update to/from views • Retrieve data from views

  3. Facts • Views as logical representation of data • Views are queried like tables • Views are objects similar to tables • Views are stored queries • Every time a view is uses the query is run (Views are not stored database)

  4. Advantages of Views • Restrict database access • Represent data from different tables • Make complex query easy • Calculate values of formula • Represent different views of the same data • Views can be created from other views

  5. Creating Views • CREATE [OR REPLACE] VIEW name AS sub-query [WITH READ ONLY]

  6. Creating Views • Example:CREATE OR REPLACE VIEW salesEmpl AS SELECT * FROM testdata.Employee WHERE dept=‘Sales’;

  7. Check the Structure of Views • DESC salesEmpl;NameNull?TypeF_Name VARCHAR2(20)L_Name VARCHAR2(20)SSN NUMBER(9)Dept VARCHAR2(20)B_Date DATE

  8. Check the Content of ViewsSELECT *FROM SalesEmpl; Retrieve data from ViewsSELECT L_Name, F_Name, SSNFROM SalesEmplWHERE TO_CHAR(B_Date, ‘YYYY’)=1973;

  9. Column Aliases:CREATE VIEW GoodStudents AS SELECT Name, SSN ID, Major Area, Email Contact FROM Students Where GPA>3; Alternative Renaming:CREATE OR REPLACE VIEW GoodStudents(Name, ID, Area, Contact)AS SELECT Name, SSN, Major, Email FROM Students WHERE GPA>3;

  10. Use of Functions: • CREATE VIEW EmployeeData(Dept, MinSal, MaxSal, AvgSal, CountEmp)AS SELECT Dept, MIN(PayRate), Max(PayRate), AVG (PayRate), Count(*) FROM Employee;

  11. Use of Functions: SELECT * FROM EmployeeData; • How to modify Views?

  12. SELECT only Views:CREATE View EmployeeDataAS SELECT L_Name, F_Name, Dept FROM EmployeeWITH READ ONLY; Why do we need a read only view?

  13. Delete Views: DROP VIEW Name) DROP VIEW EmployeeData;

  14. Check the list of viewsSELECT *FROM USER_VIEWS;

  15. INSERT Data into ViewINSERT INTO GoodStudent (ID, Name, Area, Contact) VALUES (211202111, ‘John Smith’, ‘COSC’, ‘Jsmith@fsu.edu’);

  16. Insert with NULL value: INSERT INTO GoodStudent (ID, Name, Area, Contact)VALUES (211202111, ‘John Smith’, NULL, ‘Jsmith@fsu.edu’);

  17. Delete data from views: DELETE GoodStudentWHERE ID=211202111; Update Views:UPDATE GoodStudentSET Area=‘MATH’WHERE ID=211202111;

  18. Create Views from Multiple table • CREATE OR REPLACE VIEW SalesInfo (Name, ID, Item, Cost)AS SELECT F_Name || ‘ ‘ || L_Name, ID, HowMany, Price FROM Employee, Sales WHERE ID=E_ID;

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