Relational algebra ppt
- 2. X ⋈
- 3. • 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 various operation to perform this action. • Relational algebra operations are performed recursively on a relation. • The output of these operations is a new relation, which might be formed from one or more input relations.
- 4. X ⋈
- 5. 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.
- 6. The projection eliminates all attributes of the input relation but those mentioned in the projection list. The projection method defines a relation that contains a vertical subset of Relation. This helps to extract the values of specified attributes to eliminates duplicate values. ( ) The symbol used to choose attributes from a relation. This operation helps you to keep specific columns from a relation and discards the other columns.
- 7. ID Name Address Hobby 1123 John 123 Main Stamps 1123 John 123 Main Coins 5556 Mary 7 Lake Dr Hiking 9876 Bart 5 Pine St Stamps ID Name Address Hobby 1123 John 123 Main Stamps 9876 Bart 5 Pine St Stamps Name Hobby John Stamps John Coins Mary Hiking Bart Stamps Person σ Hobby =‘stamps’(Person) Name, Hobby(Person)
- 8. UNION is symbolized by ∪ symbol. It includes all tuples that are in tables A or in B. It also eliminates duplicate tuples. So, set A UNION set B would be expressed as: The result <- A ∪ B For a union operation to be valid, the following conditions must hold -R and S must be the same number of attributes. Attribute domains need to be compatible. Duplicate tuples should be automatically removed.
- 9. A 1 B 2 D 3 F 4 E 5 A 1 C 2 D 3 E 4 A 1 B 2 C 2 D 3 E 5 F 4 E 4 A B A U B
- 10. An intersection is defined by the symbol ∩ For Ex. A ∩ B It defines a relation consisting of a set of all tuple that are in both A and B. However, A and B must be union-compatible.
- 11. A A 1 B 2 D 3 F 4 E 5 A 1 C 2 D 3 E 4 B A ∩ B A 1 D 3
- 12. X This type of operation is helpful to merge columns from two relations. Generally, a Cartesian product is never a meaningful operation when it performs alone. However, it becomes meaningful when it is followed by other operations. Cartesian Product operation denoted by X.
- 13. A A 1 B 2 D 3 F 4 E 5 A 1 C 2 D 3 E 4 B A 1 A 1 A 1 C 2 A 1 D 3 A 1 E 4 B 2 A 1 B 2 C 2 B 2 D 3 B 2 E 4 D 3 A 1 D 3 C 2 D 3 D 3 D 3 E 4 A X B F 4 A 1 F 4 C 2 F 4 D 3 F 4 E 4 E 5 A 1 E 5 C 2 E 5 D 3 E 5 E 4
- 14. Join operation is essentially a Cartesian product followed by a selection criterion. Join operation denoted by ⋈. JOIN operation also allows joining variously related tuples from different relations. Types of JOIN: Various forms of join operation are: • Inner Joins: Theta join EQUI join Natural join • Outer join: Left Outer Join Right Outer Join Full Outer Join
- 15. A Col a Col b A 1 B 2 D 3 F 4 E 5 A 1 C 2 D 3 E 4 B Col a Col b A ⋈ B A.Col a = B.Col a A ⋈ B A.Col b = B.Col b A 1 A 1 D 3 D 3 E 5 E 4 A 1 A 1 B 2 C 2 D 3 D 3 F 4 E 4
- 16. 1. Who is the father of DBMS? Ans :- Edgar. F. Codd. 2. Which is used to denote the selection operation in relational algebra? Ans :- Sigma (Greek) 3. How is the left outer join symbol represented in relational algebra? a) ⟕ b) ⟖ c) ⟗ d) ⋈ Ans :- (a) ⟕.