sql views chapter 3a. appendix objectives learn basic sql statements for creating views learn basic...
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Appendix Objectives
• Learn basic SQL statements for creating views
• Learn basic SQL statements for using views
• Understand the reasons for using views
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
• However, Oracle allows you to create the views that contain an ORDER BY clause
SQL CREATE VIEW Statement
• The SQL CREATE VIEW statement is used to create view structures.
CREATE VIEW ViewName AS
{SQL SELECT statement};
SQL CREATE VIEW Example
Create a view to list the city and product name for each product ordered by its quantity:
create view v_products as
select city, pname as myname from products order by quantity;
Using an SQL SELECT Statement
• Once the view is created, it can be used in the FROM clause of SELECT statements just like a table.
select * from v_products;
Some Uses for SQL Views
• Hide columns or rows• Display results of computations• Hide complicated SQL syntax• Layer built-in functions
Using SQL Views: Hide columns or rows I
Why do we want to hide columns/rows?1. simplify results2. security reasons
prevent the display of sensitive data
CREATE VIEW BasicDepartmentDataView AS SELECT DepartmentName,
Phone AS DepartmentPhone FROM DEPARTMENT;
SELECT * FROM BasicDepartmentDataViewORDER BY DepartmentName;
Using SQL Views: Hide columns or rows II
How do we hide rows?•Using WHERE clause
CREATE VIEW MarkingDepartmentProjectView AS SELECT ProjectID, Name AS ProjectName,
MaxHours, StartDate, EndDate FROM PROJECT WHERE Department = 'Marketing';
SELECT * FROM MarkingDepartmentProjectViewORDER BY ProjectID;
Using SQL Views: Display results of computations – SQL Statement
CREATE VIEW ProjectHoursToDateView ASSELECT PROJECT.ProjectID,
Name AS ProjectName,MaxHours AS ProjectMaxHours,SUM(HoursWorked) AS ProjectHoursWorkedToDate
FROM PROJECT, ASSIGNMENTWHERE PROJECT.ProjectID =
ASSIGNMENT.ProjectIDGROUP BY PROJECT.ProjectID;
Using SQL Views: Display results of computations – Results
SELECT * FROM ProjectHoursToDateViewORDER BY PROJECT.ProjectID;
Using SQL Views: Hide complicated SQL syntax – SQL Statement
CREATE VIEW EmployeeProjectHoursWorkedView ASSELECT Name, FirstName, LastName,
HoursWorkedFROM EMPLOYEE AS E JOIN ASSIGNMENT AS A
ON E.EmployeeNumber =A.EmployeeNumber
JOIN PROJECT AS PON A.ProjectID =
P.ProjectID;
Using SQL Views: Hide complicated SQL syntax – Results
SELECT * FROM EmployeeProjectHoursWorkedView;
Using SQL Views: Layering Computations and Built-in Functions
1st SQL Statement
CREATE VIEW ProjectHoursToDateView ASSELECT PPOJECT.ProjectID,
Name AS ProjectName,MaxHours AS ProjectMaxHours,SUM(HoursWorked) AS
ProjectHoursWorkedToDateFROM PROJECT, ASSIGNMENTWHERE PROJECT.ProjectID =
ASSIGNMENT.ProjectIDGROUP BY PROJECT.ProjectID;
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;
Using SQL Views: Layering Computations and Built-in Functions
Results
SELECT ProjectID, ProjectName, ProjectMaxHours, ProjectHoursWorkedToDate, (ProjectHoursWorkedToDate
- ProjectMaxHours) AS HoursOverMaxAllocated
FROM ProjectsOverAllotedMaxHoursViewORDER BY ProjectID;
SQL ViewsEnd of Presentation on Chapter 3A
DAVID M. KROENKE and DAVID J. AUER
DATABASE CONCEPTS, 5th Edition
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of America.
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall
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