techniques for manipulating relational data
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Techniques for Manipulating Relational Data. By Herbert A. Evans. Definition Terms. DDL (data definition language) - of a relational system is used to define the database’s attributes, tables, relationships, and indexes. - PowerPoint PPT PresentationTRANSCRIPT
Techniques for Manipulating Relational Data
By Herbert A. Evans
Definition Terms
• DDL (data definition language) - of a relational system is used to define the database’s attributes, tables, relationships, and indexes.
• DML (data manipulation language) – is used to extract, insert, and modify the information content of the database.
What is SQL?
• The DML that is of most interest to us is the SQL (Structured Query Language)
• SQL specifies the manipulation of relations by describing the results of queries, but does not give specific strategies for executing queries.
Requiring a Formal Model
• We need a formal model that is sufficiently powerful to allow optimization of queries.
• Relational algebra is that formal model!
What does relational algebra operators do?
• Reduce the number of tuples in a set by selecting those that satisfy some criteria (selection operators).
• Reduce the size of each tuple in a set by eliminating specific attributes (projection operators).
• Manipulate two similar sets of tuples by combining or comparing (set operators).
• Increase the size of each tuple by adding attributes (join and product operations).
Find all customers whose last name is “Doe”
Customer
account id last Name first Name street city state zipcode balance
101 Block Jane 345 R Cir. Apopka FL 30458- $0.00
102 Hamilton Cherry 3230 D St. Dade City FL 30555- $3.00
103 Harrison Katherine 103 L Hall Bratt FL 30457- $31.00
104 Breaux Carroll 76 M St. Apopka FL 30458- $35.00
106 Morehouse Anita 9501 L St. Houma LA 44099- $0.00
111 Doe Jane 123 M St. Apopka FL 30458- $0.00
201 Greaves Joseph 14325 N St. Godfrey IL 43580- $0.00
444 Doe Jane D rm 142 Tallahassee FL 32306- $10.55
Using selection operator to solve the previous task
• Relational algebra expression would be lastName=‘DOE’(Customer)
• The new relation results from a selection that has the same attributes as the input relation, but may have fewer rows.
Result of finding all customers whose last name is “Doe”
account Id firstName lastName street city state zipcode balance
111 Jane Doe 123 M St. Apopka FL 34331 0
444 Jane Doe D rm 142 Tallahassee FL 32306 10.55
Find all employees whose ssn is 376-77-0099 and who were employed after march 1, 1998
TimeCard
ssn date startTime endTime storeId paid
145-09-0967 1/14/1999 8:15 12:00 3 yes
245-11-4554 1/14/1999 8:15 12:00 3 yes
376-77-0099 2/23/1999 14:00 22:00 5 yes
145-09-0967 1/16/1999 8:15 12:00 3 yes
376-77-0099 1/3/1999 10:00 14:00 5 yes
376-77-0099 1/3/1999 15:00 19:00 5 yes
Using selection operator to solve previous task
• Relational algebra expression would be ssn=‘376-77-0099’ and date > ’01-mar-1999’(TimeCard)
• The new relation results from a selection that has the same attributes as the input relation, but may have fewer rows.
Result of finding all employees whose ssn is 376-77-0099 and who were employed after march 1,
1998
ssn date startTime endTime storeId paid
376-77-0099 2/23/1999 14:00 22:00 5 yes
376-77-0099 1/3/1999 10:00 14:00 5 yes
376-77-0099 1/3/1999 15:00 19:00 5 yes
List the first and last names of all customers
Customer
account id last Name first Name street city state zipcode balance
101 Block Jane 345 R Cir. Apopka FL 30458- $0.00
102 Hamilton Cherry 3230 D St. Dade City FL 30555- $3.00
103 Harrison Katherine 103 L Hall Bratt FL 30457- $31.00
104 Breaux Carroll 76 M St. Apopka FL 30458- $35.00
106 Morehouse Anita 9501 L St. Houma LA 44099- $0.00
111 Doe Jane 123 M St. Apopka FL 30458- $0.00
201 Greaves Joseph 14325 N St. Godfrey IL 43580- $0.00
444 Doe Jane D rm 142 Tallahassee FL 32306- $10.55
Using Projection Operator to Solve Previous Task
• Relational algebra expression would be lastName, firstName(Customer)
• The equivalent SQL expression would be select lastName, firstName from Customer
Result of listing the first and last names of all customers
lastName firstName
Morehouse Anita
Block Jane
Breaux Carroll
Hamilton Cherry
Harrison Catherine
Doe Jane
Greaves Joseph
What are Set Operators?
• When two relations have the same shape, that is, when the types of the attributes are the same, we can apply the usual set operators to the relations.
• This includes union, intersection, and difference.
Explanation of Set Operators
• The union of two relations is a relation that contains the set of each tuple that is in at least one of the input relations.
• The intersection of two relations is the set of all tuples that occur in both input relations.
• The difference between two relations is the set of all tuples that are in the first relation but not in the second.
Set Operator Examples
Product Operators
• The simplest product operator is the Cartesian Product.
• It produces a tuple of the new relation for each combination of one tuple from the left operand and one tuple from the right operand.
Employee x TimeCard
Employee
ssn lastName firstName
145-09-0967 Uno Jane
245-11-4554 Toulouse Jennifer
376-77-0099 Threat Ayisha
479-98-0098 Fortune Bruce
588-99-0093 Fivozinsky Bruce
TimeCard
ssn date startTime endTime storeId paid
145-09-0967 1/14/1999 8:15 12:00 3 yes
245-11-4554 1/14/1999 8:15 12:00 3 yes
376-77-0099 2/23/1999 14:00 22:00 5 yes
145-09-0967 1/16/1999 8:15 12:00 3 yes
376-77-0099 1/3/1999 10:00 14:00 5 yes
376-77-0099 1/3/1999 15:00 19:00 5 yes
Partial Result of Employee.ssn=TimeCard.ssn(Employee X TimeCard)
Employee.ssn lastName
firstName
TimeCard.ssn date
startTime
endTime storeId paid
145-09-0967 Uno Jane
145-09-0967 1/14/1999 8:15 12:00 3 no
245-11-4554 Toulouse Jie
245-11-4554 1/14/1999 8:15 12:00 3 no
145-09-0967 Uno Jane
376-77-0099 2/23/1999 14:00 22:00 5 no
245-11-4554 Toulouse Jie
145-09-0967 1/14/1999 8:15 12:00 3 no
Join operators
• It is expressed as those rows in the product whose specified fields match.
• It puts together related objects from two relations.
Employee natural joinssn TimeCard
Employee
ssn lastName firstName
145-09-0967 Uno Jane
245-11-4554 Toulouse Jennifer
376-77-0099 Threat Ayisha
479-98-0098 Fortune Bruce
588-99-0093 Fivozinsky Bruce
TimeCard
ssn date startTime endTime storeId paid
145-09-0967 1/14/1999 8:15 12:00 3 yes
245-11-4554 1/14/1999 8:15 12:00 3 yes
376-77-0099 2/23/1999 14:00 22:00 5 yes
145-09-0967 1/16/1999 8:15 12:00 3 yes
376-77-0099 1/3/1999 10:00 14:00 5 yes
376-77-0099 1/3/1999 15:00 19:00 5 yes
Result of natural joinssn TimeCard
ssn lastNamefirstNam
e datestartTim
eendTim
e storeId paid
145-09-0967 Uno Jane 1/14/1999 8:15 12:00 3 no
145-09-0967 Uno Jane 1/16/1999 8:15 12:00 3 no
245-11-4554 Toulouse Jie 1/14/1999 8:15 12:00 3 no
376-77-0099 Threat Ayisha 2/23/1999 14:00 22:00 5 no
376-77-0099 Threat Ayisha 1/3/1999 10:00 14:00 5 no
376-77-0099 Threat Ayisha 1/3/1999 15:00 19:00 5 no
Division Operator
• It is used to find objects that match every element of another set of objects.
Example of Division operator
References
• Riccardi, Greg. Principles of DATABASE SYSTEMS with Internet and Java Applications: Addision Wesley, 2001.
• Dr. Lee’s relational algebra lecture