Chapter 4 Relational Algebra

Agenda Relational Languages Relational Algebra

Relational Languages Procedural language –Relational algebra Non-procedural language –Relational Calculus Other Languages –Transform-oriented languages –Graphical languages –Fourth-generation languages –Fifth-generation languages

Relational Algebra Intra Relation  Selection - horizontal partition –SELECT relation WHERE condition [GIVING relation] –  condition (relation)  Projection - vertical partition –PROJECT relation OVER (attribute, attribute,...)[GIVING relation] –  attributes (relation)

Union-Compatible  Union - tuples in either of 2 union compatible relations –relation1 UNION relation2 [GIVING relation] –relation1  relation2  Difference - tuples in one union compatible relation, but not other —relation1 MINUS relation2 [GIVING relation] —relation1 - relation2

Union-Compatible  Intersection - tuples in both of 2 union compatible relations –relation1 INTERSECT relation2 [GIVING relation] –relation1  relation2

Any 2 Relations  Product - Cartesian product of any two relations –relation1 TIMES relation2 [GIVING relation] –relation1  relation2  Join - common domain –relation1 JOIN relation2 WHERE condition [GIVING relation] –relation1  condition  relation2 Division - same pattern –relation1 divided by relation2 [GIVING relation] –relation1 / relation2

Types of Join  Equi - based on equality with 2 identical attribute columns  Theta - a join based on a relational operator (=,, =,~=)  Natural - equijoin with no duplicate column  Outer - includes tuples without matches (left, right, full)

Types of Outer Join Left outer join - including every tuple of the left (first) relation in the solution Right outer join - including every tuple of the right (second) relation in the solution Full outer join - including every tuple of the left (first) relation and right (second) relation in the solution

Types of Join Semi-join: only the tuple of the left (first) relation with match –relation1 SEMIJOIN relation2 WHERE condition [GIVING relation] –relation1 lx condition relation2 Semi-theta-join Semi-natural join

Division Examples

Relation RRelation CRelation T1 1JJ1 1KK3 1LL 2J 2K 3L 3J 3K

Relation RRelation CRelation T1 JonesB.S. Jensen B.S.M.S. JensenM.S.Ph.D. JensenPh.D. SmithB.S. Jensen SmithM.S. Smith RogerB.S. RogerPh.D.B.S.Jones Jensen Smith Roger

Points To Remember Relational Languages Relational Algebra

Assignment Review chapters 1-4, appendix c Read Chapters 5-6 Do Exercise 4.12 (only relational algebra) and 4.13 Due date: Exam date: