Relational model
- 1. DATABASE SYSTEMS STAFF NAME : D.SARITHA ASSISTANT PROFESSOR DEPARTMENT OF COMPUTER APPLICATIONS BON SECOURS COLLEGE FOR WOMEN THANJAVUR UNIT : II CHAPTER : 2 TOPIC : RELATIONAL MODEL
- 3. ROLL_NO NAME ADDRESS PHONE AGE 1 RAM DELHI 9455123451 18 2 RAMESH GURGAON 9652431543 18 3 SUJIT ROHTAK 9156253131 20 4 SURESH DELHI 18 What is Relational Model? Relational Model represents how data is stored in Relational Databases. A relational database stores data in the form of relations (tables). Consider a relation STUDENT with attributes ROLL_NO, NAME, ADDRESS, PHONE and AGE shown in Table STUDENT
- 4. 1 RAM DELHI 9455123451 18 IMPORTANT TERMINOLOGIES 1.Attribute: Attributes are the properties that define a relation. e.g.; ROLL_NO, NAME 2.Relation Schema: A relation schema represents name of the relation with its attributes. e.g.; STUDENT (ROLL_NO, NAME, ADDRESS, PHONE and AGE) is relation schema for STUDENT. If a schema has more than 1 relation, it is called Relational Schema. 3.Tuple: Each row in the relation is known as tuple. The above relation contains 4 tuples, one of which is shown as: 4.Relation Instance: The set of tuples of a relation at a particular instance of time is called as relation instance.
- 5. ROLL_NO 1 2 3 4 5.Degree: The number of attributes in the relation is known as degree of the relation. The STUDENT relation defined above has degree 5. 6.Cardinality: The number of tuples in a relation is known as cardinality. The STUDENT relation defined above has cardinality 4. 7.Column: Column represents the set of values for a particular attribute. The column ROLL_NO is extracted from relation STUDENT. 8.NULL Values: The value which is not known or unavailable is called NULL value. It is represented by blank space. e.g.; PHONE of STUDENT having ROLL_NO 4 is NULL.
- 6. Different Types of Keys in Relational Model
- 7. Super Key The set of attributes which can uniquely identify a tuple is known as Super Key. For Example, STUD_NO, (STUD_NO, STUD_NAME) etc. Candidate Key The minimal set of attribute which can uniquely identify a tuple is known as candidate key. For Example, STUD_NO in STUDENT relation. There can be more than one candidate key in a relation. For Example, STUD_NO as well as STUD_PHONE both are candidate keys for relation STUDENT.
- 8. Primary Key There can be more than one candidate key in a relation out of which one can be chosen as primary key. For Example, STUD_NO , STUD_PHONE - candidate keys for relation STUDENT STUD_NO - primary key (only one out of many candidate keys). Alternate Key The candidate key other than primary key is called as alternate key. For Example, STUD_NO , STUD_PHONE - candidate keys for relation STUDENT STUD_NO - primary key and STUD_PHONE - alternate key
- 9. Foreign Key If an attribute can only take the values which are present as values of some other attribute, it will be foreign key to the attribute to which it refers. For Example, STUD_NO in STUDENT_COURSE is a foreign key to STUD_NO in STUDENT relation.
- 10. What is Relational Algebra? • Relational algebra is a widely used procedural query language. • It collects instances of relations as input and gives occurrences of relations as output. • It uses operators to perform queries. An operator can be either unary or binary. • It uses various operation to perform this action.
- 11. The fundamental operations of relational algebra Select Project Union Set different Cartesian product Rename
- 12. • The SELECT operation is used for selecting a subset of the tuples according to a given selection condition. • Sigma(σ) Symbol denotes it. • It is used as an expression to choose tuples which meet the selection condition. Select operation selects tuples that satisfy a given predicate. σp (r) σ is the predicate R stands for relation which is the name of the table p is prepositional logic SELECT (σ)
- 13. ROLL_NO SPORTS 1 Badminton 2 Cricket 2 Badminton 4 Badminton EMP_NO NAME ADDRESS PHONE AGE 1 RAM DELHI 9455123451 18 5 NARESH HISAR 9782918192 22 6 SWETA RANCHI 9852617621 21 4 SURESH DELHI 9156768971 18 Table 1 : EMPLOYEE Table 2 : STUDENT_SPORTS
- 14. ROLL_NO NAME ADDRESS PHONE AGE 1 RAM DELHI 9455123451 18 2 RAMESH GURGAON 9652431543 18 3 SUJIT ROHTAK 9156253131 20 4 SURESH DELHI 9156768971 18 Table 3 : STUDENT
- 15. ROLL_NO NAME ADDRESS PHONE AGE 3 SUJIT ROHTAK 9156253131 20 Eg: σ (AGE>18)(STUDENT) RESULT:
- 16. ROLL_NO NAME 1 RAM 2 RAMESH 3 SUJIT 4 SURESH Projection Operator (∏) Projection operator is used to project particular columns from a relation. SYNTAX: ∏(Column 1,Column 2….Column n)(Relation Name) EG: ∏(ROLL_NO,NAME)(STUDENT) RESULT
- 17. Cross Product(X) Cross product is used to join two relations. For every row of Relation1, each row of Relation2 is concatenated. Syntax: Relation1 X Relation2 Eg: STUDENT X STUDENT_SPORTS
- 18. ROLL_NO NAME ADDRESS PHONE AGE ROLL_NO SPORTS 1 RAM DELHI 9455123451 18 1 Badminton 1 RAM DELHI 9455123451 18 2 Cricket 1 RAM DELHI 9455123451 18 2 Badminton 1 RAM DELHI 9455123451 18 4 Badminton 2 RAMESH GURGAON 9652431543 18 1 Badminton 2 RAMESH GURGAON 9652431543 18 2 Cricket 2 RAMESH GURGAON 9652431543 18 2 Badminton 2 RAMESH GURGAON 9652431543 18 4 Badminton 3 SUJIT ROHTAK 9156253131 20 1 Badminton 3 SUJIT ROHTAK 9156253131 20 2 Cricket 3 SUJIT ROHTAK 9156253131 20 2 Badminton 3 SUJIT ROHTAK 9156253131 20 4 Badminton 4 SURESH DELHI 9156768971 18 1 Badminton 4 SURESH DELHI 9156768971 18 2 Cricket 4 SURESH DELHI 9156768971 18 2 Badminton 4 SURESH DELHI 9156768971 18 4 Badminton
- 19. Union (U) Union on two relations R1 and R2 can only be computed. Union operator when applied on two relations R1 and R2 will give a relation with tuples which are either in R1 or in R2 Syntax: Relation1 U Relation2 Eg: STUDENT U EMPLOYEE ROLL_NO NAME ADDRESS PHONE AGE 1 RAM DELHI 9455123451 18 2 RAMESH GURGAON 9652431543 18 3 SUJIT ROHTAK 9156253131 20 4 SURESH DELHI 9156768971 18 5 NARESH HISAR 9782918192 22 6 SWETA RANCHI 9852617621 21 RESULT:
- 20. Minus (-) Minus on two relations R1 and R2 can only be computed if R1 and R2 are union compatible. Minus operator when applied on two relations as R1-R2 will give a relation with tuples which are in R1 but not in R2. Syntax: Relation1 - Relation2 Eg: STUDENT - EMPLOYEE ROLL_NO NAME ADDRESS PHONE AGE 2 RAMESH GURGAON 9652431543 18 3 SUJIT ROHTAK 9156253131 20 RESULT
- 21. Rename(ρ) Rename operator is used to give another name to a relation. Syntax: ρ(Relation2, Relation1) Eg: ρ(STUDENT1, STUDENT) ρ(STUDENT_NAMES, ∏(ROLL_NO, NAME)(STUDENT))
- 22. JOIN OPERATIONS A Join operation combines related tuples from different relations, if and only if a given join condition is satisfied. It is denoted by ⋈ Example: EMP_CODE EMP_NAME 101 Stephan 102 Jack 103 Harry EMPLOYEE EMP_CODE SALARY 101 50000 102 30000 103 25000 SALARY Operation: (EMPLOYEE ⋈ SALARY)
- 23. EMP_CODE EMP_NAME SALARY 101 Stephan 50000 102 Jack 30000 103 Harry 25000 Result
- 25. EMP_NAME SALARY Stephan 50000 Jack 30000 Harry 25000 •A natural join is the set of tuples of all combinations in R and S that are equal on their common attribute names. •It is denoted by ⋈. Example: ∏ EMP_NAME, SALARY (EMPLOYEE ⋈ SALARY) Output: NATURAL JOIN
- 26. EMP_ NAME STREET CITY Ram Civil line Mumbai Shyam Park street Kolkata Ravi M.G. Street Delhi Hari Nehru nagar Hyderabad EMP_ NAME BRANCH SALARY Ram Infosys 10000 Shyam Wipro 20000 Kuber HCL 30000 Hari TCS 50000 The outer join operation is an extension of the join operation. It is used to deal with missing information. Example OUTER JOIN FACT_WORKERSEMPLOYEE
- 27. EMP_NAME STREET CITY BRANCH SALARY Ram Civil line Mumbai Infosys 10000 Shyam Park street Kolkata Wipro 20000 Hari Nehru nagar Hyderabad TCS 50000 (EMPLOYEE ⋈ FACT_WORKERS) Output
- 28. EMP_NAME STREET CITY BRANCH SALARY Ram Civil line Mumbai Infosys 10000 Shyam Park street Kolkata Wipro 20000 Hari Nehru street Hyderabad TCS 50000 Ravi M.G. Street Delhi NULL NULL •Left outer join contains the set of tuples of all combinations in R and S that are equal on their common attribute names. •In the left outer join, tuples in R have no matching tuples in S. •It is denoted by ⟕. Example EMPLOYEE ⟕ FACT_WORKERS LEFT OUTER JOIN
- 29. EMP_NAME BRANCH SALARY STREET CITY Ram Infosys 10000 Civil line Mumbai Shyam Wipro 20000 Park street Kolkata Hari TCS 50000 Nehru street Hyderabad Kuber HCL 30000 NULL NULL • Right outer join contains the set of tuples of all combinations in R and S that are equal on their common attribute names. • In right outer join, tuples in S have no matching tuples in R. • It is denoted by ⟖. Example: EMPLOYEE ⟖ FACT_WORKERS Output: RIGHT OUTER JOIN
- 30. EMP_NAME STREET CITY BRANCH SALARY Ram Civil line Mumbai Infosys 10000 Shyam Park street Kolkata Wipro 20000 Hari Nehru street Hyderabad TCS 50000 Ravi M.G. Street Delhi NULL NULL Kuber NULL NULL HCL 30000 :Full outer join is like a left or right join except that it contains all rows from both tables. •In full outer join, tuples in R that have no matching tuples in S and tuples in S that have no matching tuples in R in their common attribute name. •It is denoted by ⟗. Example EMPLOYEE ⟗ FACT_WORKERS Output: FULL OUTER JOIN
- 31. CLASS_ID NAME 1 John 2 Harry 3 Jackson PRODUCT_ID CITY 1 Delhi 2 Mumbai 3 Noida CLASS_ID NAME PRODUCT_I D CITY 1 John 1 Delhi 2 Harry 2 Mumbai 3 Harry 3 Noida It is also known as an inner join. It is based on matched data as per the equality condition. The equi join uses the comparison operator(=). Example CUSTOMER ⋈ PRODUCT Output EQUI JOIN CUSTOMER PRODUCT
- 32. Relational algebra operations have been extended in various ways ¤ More generalized ¤ More useful! ¨ Three major extensions: ¤ Generalized projection ¤ Aggregate functions ¤ Additional join operations
- 33. GENERALIZED PROJECTION Written as: ∏F1, F2, …, Fn (E) ¤ Fi are arithmetic expressions ¤ E is an expression that produces a relation ¤ Derived attributes - Values are always computed from other attributes stored in database ¤ Also useful for updating values in database
- 34. GENERALIZED PROJECTION EXAMPLE ∏cred_id, (limit – balance) as available_credit (credit_acct) cred_id limit balance C-273 2500 150 C-291 750 600 C-304 15000 3500 C-313 300 25 cred_id Available_credit C-273 2350 C-291 150 C-304 11500 C-313 275 credit_acct available_acc
- 35. AGGREGATE FUNCTIONS sum - sums the values in the collection avg - computes average of values in the collection count - counts number of elements in the collection min - returns minimum value in the collection Max - returns maximum value in the collection
- 36. Gsum(balance)(credit_acct) 4275 cred_id limit balance C-273 2500 150 C-291 750 600 C-304 15000 3500 C-313 300 25 Gavg(limit)(credit_acct) 11500 Gcount(bal)(credit_acct) 4
- 39. and: (true and unknown) = unknown; (false and unknown) = false; (unknown and unknown) = unknown. or: (true or unknown) = true; (false or unknown) = unknown; (unknown or un- known) = unknown. not: (not unknown) = unknown NULL VALUES Null indicates - “value unknown or nonexistent,” any arithmetic operations (such as +, −, ∗, /) involving null values must return a null result.
- 40. MODIFICATION OF THE DATABASE Often need to modify data in a database Can use assignment operator Operations: r r U E Insert new tuples into a relation r r – E Delete tuples from a relation r P(r) Update tuples already in the relation
- 41. THANK YOU