# Relational Operators

There are 8 relational operators:

**SELECT**Selects rows from a table that have specified attribute values.**PROJECT**Selects rows made up of a subset of columns from a table.**PRODUCT**Builds a relation from two specified relations consisting of all possible combinations of rows, one from each of the two relations.**UNION**Builds a relation consisting of all rows appearing in either or both of the two relations.**INTERSECT**Builds a relation consisting of all rows appearing in both of the two relations.**DIFFERENCE**Builds a relation consisting of all rows appearing in the first and not in the second of the two relations.**DIVIDE**Takes two relations, one binary and one unary, and builds a relation consisting of all values of one column of the binary relation that match, in the other column, all values in the unary relation. Ex.**A: B:**a x xa y y

a z

b x

c y

=>

**A DIVIDE B**: a Basically, A/B = <m> such that for every n value in a tuple of B there is <m, n> in A.

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