__RELATIONAL LANGUAGES:__

__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:

**Selection**(restriction). Selection of rows E,g salary>100(staff).those employ who have- salary more than 1000in salary table ..O
_{condition }(R) e.g O_{salary>100 }(Staff) **Projection**: select columns from a relation. ∏_{col1,…….coln }(R)…… ∏_{sno,fname,address }- (Student)
**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 &- cid is the record of course table
**Union**: to join two relations…..R ⋃S

union compatible..>data type must be same .

No duplication: no duplicate rows.

**Difference**: tuples which are in R but not n S . R – S ..wat r the members which are- in one society but not n another society.
**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

**Intersection**: tuples that r n both R & S & must be union-compatible. R ⋂S**Division**: R**∻**S