1. Structured Query Language Part I Chapter Three CIS 218

2. 3-2 Structured Query Language –Acronym: SQL –Pronounced as “S-Q-L” [“Ess-Que-El”] –Also pronounced as “Sequel” Originally developed by IBM in 1970s –SEQUEL language

3. 3-3 SQL Defined SQL is not a programming language SQL is comprised of: –A data definition language (DDL) Used to define structures Tables, columns, etc. –A data manipulation language (DML) Used to create, add and delete data rows Used to retrieve (query) data

4. 3-4 SQL Queries SELECT is the best known SQL statement SELECT will retrieve information from the database that matches specified criteria Uses SELECT/FROM/WHERE syntax SELECT col1, col2, … FROM tableName WHEREcriteria;

5. 3-5 Displaying All Columns To show all of the column values for the rows that match the specified criteria, use an asterisk ( * ) SELECT * FROM Tech Returns all columns and all rows

6. 3-6 A Query Creates a Relation A query pulls information from one or more relations A query creates (temporarily) a new relation A “virtual” table

7. 3-7 Displaying a Subset of Columns To show specific columns, list the column names in the SELECT clause SELECT First, Last FROM Tech Returns two columns and all rows

8. 3-8 Displaying a Subset of Rows To filter rows, add a WHERE clause SELECT * FROM Tech WHERE PayScale = 2 Returns all columns Returns only the rows for Techs who have a PayScale of 2.

9. Practice Display all columns for all jobs Display the TicketNum, Date, and Description for all jobs Display all columns for jobs performed by TechID 1 Display the TicketNum, Date, and Description for jobs performed by TechID 1 3-9

10. 3-10 Showing Unique Values The DISTINCT keyword Added to the SELECT statement to prevent rows with duplicate values from displaying SELECT DISTINCT Location FROM Job

11. 3-11 Specifying Search Criteria The WHERE clause stipulates the matching criteria for the records that are to be displayed SELECT EmpName FROM EMPLOYEE WHERE DeptID = 15

12. 3-12 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 “<=“

13. Strings and Dates Strings need to be quoted SELECT * FROM Job WHERE Description = “Upgrade Office” Dates are represented with the “#” sign SELECT * FROM Job WHERE Date > #4/2/2007# 3-13

14. NULL values IS NULL –matches empty values SELECT * FROM Job WHERE TechID IS NULL IS NOT NULL –matches non-empty values SELECT * FROM Job WHERE TechID IS NOT NULL 3-14

15. 3-15 Logical Operators Multiple matching criteria may be specified using –AND Both conditions must be true –OR Either condition may be true

16. 3-16 Operator Examples SELECT First, Last FROM Tech WHERE PayScale > 1 AND PayScale < 3 SELECT Description FROM Job WHERE Date > #1/1/2008# OR TechID = 1

17. Practice Display the dates and descriptions for all jobs before 1/1/2008. Display the dates and descriptions for all jobs between 1/1/2007 and 1/1/2008. Display the dates and descriptions for all jobs performed by techs 1 and 2. Display the dates and descriptions for all jobs performed by techs 1, 2 or 3. 3-17

18. 3-18 A List of Values The WHERE clause may include the IN keyword Specifies that a particular column value must be included in a list of values Alternative to logical OR SELECT * FROM Job WHERE TechID IN (1, 2, 3);

19. 3-19 The Logical NOT Operator Any criteria statement may be preceded by a NOT operator All information will be shown except the information matching the specified criteria SELECT * FROM Job WHERE TechID NOT IN (1, 2, 3);

20. 3-20 Finding Data in a Range of Values BETWEEN keyword Allows a user to specify a minimum and maximum value SELECT * FROM Tech WHERE PayScale BETWEEN 1 AND 3; Alternative to: –PayScale >= 1 AND PayScale <= 3

21. 3-21 Wildcard Searches SQL LIKE keyword Allows searches on partial data values LIKE can be paired with wildcards to find rows matching a string value –Multiple character wildcard character asterisk (*) –Single character wildcard character question mark (?)

22. 3-22 Wildcard Search Examples SELECTFirst, Last FROM Tech WHERE Last LIKE ‘B????' SELECT * FROM Job WHERE Description LIKE ‘*printer*’

23. 3-23 Sorting the Results Query results may be sorted using the ORDER BY clause SELECT * FROM Job ORDER BY Description Use DESC to sort in descending order ORDER BY Description DESC

24. 3-24 Built-in SQL 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 –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

25. 3-25 Built-in Function Examples SELECT COUNT(TechID) FROM Job SELECT MIN(PayScale) AS Minimum_Scale, MAX(PayScale) AS Maximum_Scale, AVG(PayScale) AS Average_Scale FROM Tech

26. 3-26 Providing Subtotals Subtotals may be calculated by using the GROUP BY clause The HAVING clause may be used to restrict which data is displayed SELECT TechID, COUNT(*) AS NumberOfJobs FROM Job GROUP BY TechID HAVING COUNT(*) >= 2;

27. 3-27 Retrieving Information from Multiple Tables Joins –Combines data across tables SELECT Date, Description, First, Last FROM Tech, Job WHERE Tech. ID = Job.TechID SELECT Date, Description, First, Last FROM Tech, Job WHERE Tech. ID = Job.TechID ANDLast = “Bowers”

28. Practice Display the names of techs whose first names start with A Display the names of all techs, sorted by last name Count how many jobs have been completed Display the names of the techs who completed jobs in 2007. 3-28