Database Relational Algebra



It’s a theoratical langauge which wth operations work on one or more relations to define another

relation without changing thte original relation…

FACILITIES: (operations) of relational algebra:

  1. Selection(restriction). Selection of rows E,g salary>100(staff).those employ who have
  2. salary more than 1000in salary table ..O condition  (R) e.g O salary>100  (Staff)
  3. Projection: select columns from a relation. col1,…….coln (R)…… sno,fname,address
  4. (Student)
  5. Cartesian Product: concatinate rows of one relation to other relation’s record. R * S.. (Sid,name)(strudent)*(cid)(courses)..sid , name are the record of student relations &
  6. cid is the record of course table
  7. Union: to join two relations…..R ⋃S

        union compatible..>data type must be same .

        No duplication: no duplicate rows.

  1. Difference: tuples which are in R but not n S . R – S ..wat r the members which are
  2. in one society but not n another society.
  3. Joins Operators: joining of two relations. Join operators are
    • Theta Join :matching of two field in two relation. It include =,<,><=,=!…..R ⋈condition S
    • Equi join: Teta is general form so for equal it s equal join, for the greater it s greater
    • join.
    • Natural join: if there are two columns that will become one.
    • Outer join: those which are matching & those which are not matching that is complete
    • relation. ⊳⊲
    • Semi join: DDB(distributd DB) take relations from one side & then relations from other
    •  side.  R ⊳f S…where f s  condition or predicate. protocol
  4. Intersection: tuples that r n both R & S & must be union-compatible. R ⋂S
  5. Division : R S