© 2002 by Prentice Hall 1 Structured Query Language David M. Kroenke Database Concepts 1e Chapter 3 3

© 2002 by Prentice Hall2 Chapter Objectives Learn basic SQL statements for creating database constructs Learn basic SQL SELECT statements and options for processing a single table Learn basic SQL SELECT statements for processing multiple tables with subqueries Learn basic SQL SELECT statements for processing multiple tables with joins Learn SQL statements to add, modify, and delete data

© 2002 by Prentice Hall3 Structured Query Language Structured Query Language is known as either: –Its acronym, SQL, or –SEQUEL, the name of the original version of SQL SEQUEL was developed by IBM in the mid- 1970s.

© 2002 by Prentice Hall4 SQL Defined SQL is not a programming language, but rather a data sub-language SQL has several functions –Data Definition –Data Retrieval (Queries) –Data Manipulation/Updates –And others (not covered in this chapter) Data control Transaction control

© 2002 by Prentice Hall5 SQL for Data Definition The SQL data definition statements include –CREATE To create database objects –ALTER To modify the structure and/or characteristics of database objects –DROP To delete database objects

© 2002 by Prentice Hall6 SQL for Data Definition: CREATE Creating database tables –The SQL CREATE TABLE statement CREATE TABLE Employee ( EmpID Integer Not Null, EmpName Char(25));

© 2002 by Prentice Hall7 Primary Key Constraint: ALTER Adding primary key constraints to an existing table –The SQL ALTER statement ALTER TABLE Employee ADD CONSTRAINT EmpPK PRIMARY KEY(EmpID);

© 2002 by Prentice Hall8 Composite Primary Key Constraints: ALTER The SQL ALTER statement may also be used to create a composite primary key constraint CREATE TABLE Empl_Skill ( EmpID Integer Not Null, SkillID Integer Not Null, SkillLevel Integer); ALTER TABLE Empl_Skill ADD CONSTRAINT EmpSkillPK PRIMARY KEY(EmpID, SkillID);

© 2002 by Prentice Hall9 Foreign Key Constraint: ALTER Adding foreign key constraints to an existing table –The SQL ALTER statement ALTER TABLE Employee ADD CONSTRAINT EmpFK FOREIGN KEY(DeptID) REFERENCES Dept;

© 2002 by Prentice Hall10 Defining the Cascade Rules: ALTER Using the SQL ALTER statement to apply cascading rules ALTER TABLE Employee ADD CONSTRAINT EmpFK FOREIGN KEY(DeptID) REFERENCES Dept ON DELETE CASCADE;

© 2002 by Prentice Hall11 Deleting Database Objects: DROP To remove unwanted database objects from the database, use the SQL DROP statement Warning… The DROP statement will permanently remove the object and all data DROP TABLE Employee;

© 2002 by Prentice Hall12 Removing a Constraint: ALTER & DROP To change the constraints on existing tables, you may need to remove the existing constraints before adding new constraints ALTER TABLE Employee DROP CONSTRAINT EmpFK;

© 2002 by Prentice Hall13 SQL for Data Retrieval (Queries) The most well known SQL statement… SELECT SELECT will retrieve information from the database that matches the specified criteria SELECT EmpName FROM Emp;

© 2002 by Prentice Hall14 The Results of a Query is a Relation A query pulls information from several relations and creates (temporarily) a new relation This allows for a query to: –Create a new relation –Feed information to another query (sub- queries)

© 2002 by Prentice Hall15 Showing a Row Only Once: DISTINCT A qualifier may be added to the SELECT statement to inhibit duplicate rows from displaying SELECT DISTINCT DeptID from Emp;

© 2002 by Prentice Hall16 Specifying Search Criteria: WHERE The WHERE clause stipulates the matching criteria for the record that are to be displayed SELECT EmpName FROM Emp WHERE DeptID = 15;

© 2002 by Prentice Hall17 Match Criteria The WHERE clause match criteria may include –Equals “=“ –Not Equals “<>” –Greater than “>” –Less than “<“ –Greater than or Equal to “>=“ –Less than or Equal to “<=“

© 2002 by Prentice Hall18 Match Operators Multiple matching criteria may be specified using –AND Representing an intersection of the data sets –OR Representing a union of the data sets

© 2002 by Prentice Hall19 Operator Examples SELECT EmpName FROM Emp WHERE DeptID < 7 OR DeptID > 12; SELECT EmpName FROM Emp WHERE DeptID = 9 AND SalaryCode <= 23;

© 2002 by Prentice Hall20 A List of Values The WHERE clause may specify that a particular column value must be included in a list of values SELECT EmpName FROM Emp WHERE DeptID IN (4, 8, 9);

© 2002 by Prentice Hall21 The Logical NOT Operator Any criteria statement may be preceded by a NOT operator which is to say that all information will be shown except that information matching the specified criteria SELECT EmpName FROM Emp WHERE DeptID NOT IN (4, 8, 9);

© 2002 by Prentice Hall22 Finding Data Matching a Range of Values: BETWEEN SQL provides a BETWEEN statement that allows a user to specify a minimum and maximum value on one line SELECT EmpName FROM Emp WHERE SalaryCode BETWEEN 10 AND 45;

© 2002 by Prentice Hall23 Allowing for Wildcard Searches: LIKE Sometimes it may be advantageous to find rows matching a string value using wildcards –Single character wildcard character is an underscore (_) –Multiple character wildcard character is a percent sign (%)

© 2002 by Prentice Hall24 Wildcard Search Examples SELECT EmpID FROM Emp WHERE EmpName LIKE ‘Kr%’; SELECT EmpID FROM Emp WHERE Phone LIKE ‘616-___-____’;

© 2002 by Prentice Hall25 Displaying All Columns: * To show all of the column values for the rows that match the specified criteria, use an * SELECT * FROM Emp WHERE EmpName LIKE ‘%land’;

© 2002 by Prentice Hall26 Sorting the Results: ORDER BY The results may be sorted using the ORDER BY clause SELECT * FROM Emp ORDER BY EmpName;

© 2002 by Prentice Hall27 Built-in SQL Functions SQL provides several built-in functions –COUNT Counts the number of rows that match the specified criteria –MIN Finds the minimum value for a specific column for those rows matching the criteria –MAX Finds the maximum value for a specific column for those rows matching the criteria

© 2002 by Prentice Hall28 Built-in SQL Functions (continued) SUM –Calculates the sum for a specific column for those rows matching the criteria AVG –Calculates the numerical average of a specific column for those rows matching the criteria

© 2002 by Prentice Hall29 Built-in Function Examples SELECT COUNT(DISTINCT DeptID) FROM Emp; SELECT MIN(Hours), MAX(Hours), AVG(Hours) FROM Project WHERE ProjID > 7;

© 2002 by Prentice Hall30 Providing Subtotals: GROUP BY Subtotals may be calculated by using the GROUP BY clause SELECT DeptID, COUNT(*), FROM Emp GROUP BY DeptID HAVING Count(*) > 3;

© 2002 by Prentice Hall31 Retrieving Information from Multiple Tables SubQueries –As stated earlier, the result of a query is a relation. As a result, a query may feed another query. This is called a subquery Joins –Another way of combining data is by using a Join Equi-Join Left Outer Join Right Outer Join

© 2002 by Prentice Hall32 Subquery SELECT EmpName FROM Emp WHERE DeptID in (SELECT DeptID from Department WHERE DeptName LIKE ‘Accounts%’);

© 2002 by Prentice Hall33 Equi-Join SELECT EmpName FROM Emp, Department WHERE Emp.DeptID = Department.DeptID AND Department.DeptName LIKE ‘Account%’;

© 2002 by Prentice Hall34 Outer Join Right Outer Join SELECT EmpName FROM Department RIGHT JOIN Emp WHERE Emp.DeptID = Department.DeptID AND Department.DeptName LIKE ‘Account%’; Left Outer Join SELECT EmpName FROM Emp LEFT JOIN Department WHERE Emp.DeptID = Department.DeptID AND Department.DeptName LIKE ‘Account%’;

© 2002 by Prentice Hall35 Modifying Data using SQL Insert –Will add a new row in a table Update –Will update the data in a table that matches the specified criteria Delete –Will delete the data in a table that matches the specified criteria

© 2002 by Prentice Hall36 Adding Data: INSERT To add a row to an existing table, use the INSERT statement INSERT INTO Emp VALUES (91, ‘Smither’, 12); INSERT INTO Emp (EmpID, SalaryCode) VALUES (62, 11);

© 2002 by Prentice Hall37 Changing Data Values: UPDATE To change the data values in an existing row (or set of rows) use the Update statement UPDATE Emp SET Phone ‘ ’ WHERE EmpID = 29; UPDATE Emp SET DeptID = 44 WHERE EmpName LIKE ‘Kr%’;

© 2002 by Prentice Hall38 Deleting Data: DELETE To delete a row or set of rows from a table using the DELETE statement DELETE FROM Emp WHERE EmpID = 29; DELETE FROM Emp WHERE EmpName LIKE ‘Kr%’;

© 2002 by Prentice Hall 39 Structured Query Language David M. Kroenke Database Concepts 1e Chapter 3 3