Querying Database
ISYS 363
Basic Query Language Operations
• Selection
• Projection
• Join
• Aggregates: Max, Min, Sum, Avg, Count– Totals and SubTotals– GroupBy
• Calculated fields
Selection
• Selection operation retrieves records that satisfy user’s criteria.
Criteria
• >, >=, <, <=, =, <>
• Range: BETWEEN 1/1/03 AND 12/31/03
• Wildcard:– ? – match any one character
• “K?NG”
– * - Match any number of characters• “C*”
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
Join
• The two tables must have common attributes:– Key and foreign key.
• Combines two tables to form a new table where records of the two tables are combined if the common attributes have the same value.
Join Example
Faculty File: FID FnameF1 ChaoF2 SmithF5 Boxer
Student File:SID Sname FIDS1 Peter F1S2 Paul F2S3 Smith F1
Faculty Join Student =
Join Example
Student File:SID Sname FIDS1 Peter
F1S2 Paul
F2S3 Smith
F1
StudentCourse File:SIDCIDS1ISYS263S1Acct101S3ISYS363S2ISYS263S2Fin350S2Acct101
Course File:CID Cname
UnitsISYS263 IS Intro
3ISYS363 MIS Intro
3Acct101 accounting
3Fin350 Finance Intro
3
(Student Join StudentCourse) Join Course
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?
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?
University Database
ERD Notations
Student Account
Faculty Course
Has1 1
EnrollM MAdvise
M
1
SIDSname Major SID Balance
FID Fname CID CnameUnitsPhone
Grade
GPA
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.
Top n query: Example Top 3 GPA1. Sort GPA in descending order2. From Query/Design view, click Property Sheet and select Top Value
Order Processing Database
Query Examples
– 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
Calculated Fields
• Rename a field:– NewName:OldName
• Define a calculated field:– Tax:salary*.15– Age:Year(Now()) – Year(DOB)– IIF function
Sorting
• One field sorting
• Two fields sorting
Other Queries
• Update query:– Query tools/Design/Query type/Update
• Delete query
• Parameter query
• CrossTab query– Crosstab row
Access Tools for Import/Export
• Import from Excel:– The first row of Excel’s list should contain field
names– External Data/Import/Excel
• Export to Excel:– External Data/Export/Excel
Open Database Connectivity (ODBC)
• Provide a standard to retrieve data from a database.
• It manages one or more "database drivers“ that enables the communication between database and applications.
• To access a database, we use ODBC facilities to define a ODBC data source name for the database.
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