1. Querying Database
ISYS 363

2. Basic Query Language Operations
Selection
Projection
Join
Aggregates: Max, Min, Sum, Avg, Count
Totals and SubTotals
GroupBy
Calculated fields

3. Selection
Selection operation retrieves records that satisfy user’s criteria.

4. Criteria >, >=, <, <=, =, <>
Range: BETWEEN 1/1/03 AND 12/31/03
Wildcard:
? – match any one character
“K?NG”
* - Match any number of characters
“C*”

5. Projection
Projection operation defines a vertical subset of a table and retrieves only the specified fields.
Example: Customer table: CID, Cname, City, Rating
Create a query to show CID, Cname, Rating
Create a query to show CID, Cname, City

6. Join The two tables must have common attributes:
Key and foreign key match.
Combines two tables to form a new table where records of the two tables are combined if the common attributes have the same value.

7. Join Example Faculty File: FID Fname F1 Chao F2 Smith F5 Boxer
Student File:
SID Sname FID
S1 Peter F1
S2 Paul F2
S3 Smith F1
Faculty Join Student =

8. Join Example (Student Join StudentCourse) Join Course
StudentCourse File:
SID CID
S1 ISYS263
S1 Acct101
S3 ISYS363
S2 ISYS263
S2 Fin350
S2 Acct101
Student File:
SID Sname FID
S1 Peter F1
S2 Paul F2
S3 Smith F1
Course File:
CID Cname Units
ISYS263 IS Intro 3
ISYS363 MIS Intro 3
Acct101 accounting 3
Fin350 Finance Intro 3
(Student Join StudentCourse) Join Course

9. Aggregate Functions Max, Min, Sum, Count, Avg QueryTools/Totals
Ex. Employee: EmpID,Ename, Sex, Race, Birthdate, Hiredate, Salary
How many employees in this company?
What is the overall average salary?

10. Aggregates by Group Compute the average salary by race.
Compute the average salary by sex.
Compute the average salary by Race and Sex.
How many employees in each race group?

11. University Database

12. ERD Notations 1 1 Student Has Account M M M 1 Faculty Course Enroll
Major
Sname
GPA
SID
Balance
SID 1 1
Student
Has
Account M M M
Enroll
Advise
Grade 1
Faculty
Course
Units
Phone
FID
Fname
CID
Cname

13. Query Examples
Q1: Display students’ ID, name and account balance who owe university more than $2000.
Q2: Display student’s ID, name and total units.
Q3: Find students taking at least 9 units and display their ID, Name and total units.
Q4: Display CID, Cname, SID, Sname
Q5: Display CID, Cname, number of students in each course.
Q6: Display faculty’s name and phone if the faculty advises at least three students.

14. Order Processing Database

15. Query Examples Total sales by product Total amount for each order
Find customers live in San Francisco.
Produce a customer report that shows CID, Cname, and Rating.
Number of customers in each city
City, NumbeOfCustomers
Produce a report that shows the number of orders for each customer:
CID, Cname, TotalNumberOfOrders
Total sales by product
Total amount for each order
MIS report
Criteria applied to subtotal

16. Calculated Fields Rename a field: Define a calculated field:
NewName:OldName
Define a calculated field:
Tax:salary*.15
Age:Year(Now()) – Year(DOB)
IIF function

17. Sorting
One field sorting
Two fields sorting

18. Other Queries Update query: Delete query Parameter query
Query tools/Design/Query type/Update
Delete query
Parameter query
CrossTab query
Crosstab row

19. Top n query: Example Top 3 GPA 1. Sort GPA in descending order 2
Top n query: Example Top 3 GPA 1. Sort GPA in descending order 2. From Query/Design view, click Property Sheet and select Top Value