SQL Views Appendix C DATABASE CONCEPTS, 3rd Edition DAVID M. KROENKE and DAVID J. AUER DATABASE CONCEPTS, 3rd Edition Appendix C SQL Views

Appendix Objectives Learn basic SQL statements for creating views Learn basic SQL statements for using views Understand the reasons for using views KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

SQL Views A SQL view is a virtual table that is constructed from other tables or views A view has no data of its own, but uses data stored in tables or other views Views are created using SQL SELECT statements Views are used in other SELECT statements just as if they were a table The SQL statements that create the views may not contain an ORDER BY clause If the results of a query using a view need to be sorted, the sort order must be provided by the SELECT statement that processes the view KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

SQL CREATE VIEW Statement The SQL CREATE VIEW statement is used to create view structures. CREATE VIEW ViewName AS {SQL SELECT statement}; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

SQL CREATE VIEW Example CREATE VIEW EmployeePhoneView AS SELECT FirstName, LastName, Phone AS EmployeePhone FROM EMPLOYEE; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Creating a SQL View in SQL Server 2005 Click the New Query button, enter the SQL for the view just as you would enter the SQL for a query, and then click the Execute button to create the query The “Command(s) completed successfully” message in the Messages window indicates that the view has been created The new view appears in the expanded Views folder after it is created KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Creating a SQL View MySQL 5.x Enter the SQL for the view just as you would enter the SQL for a query, and then click the Execute button to create the query The new view appears in the expanded wpc schema after it is created (you may have to refresh the schema for it to appear) The “Query returned no resultset” message indicates that the view has been created KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using an SQL CREATE Once the view is created, it can be used in the FROM clause of SELECT statements just like a table. SELECT * FROM EmployeePhoneView ORDER BY LastName; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using the EmployeePhoneView in SQL Server 2005 Click the New Query button, enter the SQL for the query that uses the view, and then click the Execute button to create the query The query results appear in the Results window. KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using the EmployeePhoneView in MySQL 5.X Enter the SQL for the query that uses the view, and then click the Execute button to create the query The query results appear in the Resultset window. Use the File | New Resultset Tab command to open a new Resultset window KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Some Uses for SQL Views Hide columns or rows Display results of computations Hide complicated SQL syntax Layer built-in functions KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Hide columns or rows I CREATE VIEW BasicDepartmentDataView AS SELECT DepartmentName, Phone AS DepartmentPhone FROM DEPARTMENT; SELECT * FROM BasicDepartmentDataView ORDER BY DepartmentName; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Hide columns or rows II CREATE VIEW MarkingDepartmentProjectView AS SELECT ProjectID, Name AS ProjectName, MaxHours, StartDate, EndDate FROM PROJECT WHERE Department = 'Marketing'; SELECT * FROM MarkingDepartmentProjectView ORDER BY ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Display results of computations – SQL Statement CREATE VIEW ProjectHoursToDateView AS SELECT PROJECT.ProjectID, Name AS ProjectName, MaxHours AS ProjectMaxHours, SUM(HoursWorked) AS ProjectHoursWorkedToDate FROM PROJECT, ASSIGNMENT WHERE PROJECT.ProjectID = ASSIGNMENT.ProjectID GROUP BY PROJECT.ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Display results of computations - Results SELECT * FROM ProjectHoursToDateView ORDER BY PROJECT.ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Hide complicated SQL syntax – SQL Statement CREATE VIEW EmployeeProjectHoursWorkedView AS SELECT Name, FirstName, LastName, HoursWorked FROM EMPLOYEE AS E JOIN ASSIGNMENT AS A ON E.EmployeeNumber = A.EmployeeNumber JOIN PROJECT AS P ON A.ProjectID = P.ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Hide complicated SQL syntax - Results SELECT * FROM EmployeeProjectHoursWorkedView; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Layering Computations and Built-in Functions 1st SQL Statement CREATE VIEW ProjectHoursToDateView AS SELECT PPOJECT.ProjectID, Name AS ProjectName, MaxHours AS ProjectMaxHours, SUM(HoursWorked) AS ProjectHoursWorkedToDate FROM PROJECT, ASSIGNMENT WHERE PROJECT.ProjectID = ASSIGNMENT.ProjectID GROUP BY PROJECT.ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Layering Computations and Built-in Functions 2nd SQL Statement CREATE VIEW ProjectsOverAllotedMaxHoursView AS SELECT ProjectID, ProjectName, ProjectMaxHours, ProjectHoursWorkedToDate FROM ProjectHoursToDateView WHERE ProjectHoursWorkedToDate > ProjectMaxHours; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

Using SQL Views: Layering Computations and Built-in Functions Results SELECT ProjectID, ProjectName, ProjectMaxHours, ProjectHoursWorkedToDate, (ProjectHoursWorkedToDate - ProjectMaxHours) AS HoursOverMaxAllocated FROM ProjectsOverAllotedMaxHoursView ORDER BY ProjectID; KROENKE and AUER - DATABASE CONCEPTS (3rd Edition) © 2008 Pearson Prentice Hall

End of Presentation on Appendix C DAVID M. KROENKE and DAVID J. AUER DATABASE CONCEPTS, 3rd Edition End of Presentation on Appendix C SQL Views