Project

Keeps only a subset of attributes.

Signature

project(operand: Relation, attributes: AttrList) -> Relation

Examples

project(suppliers, [:city])

project(suppliers, [:city], allbut: true)

Description

Computes the relation obtained by projecting tuples from operand on a subset of their attributes.

This operator supports an ALL BUT variant, through the allbut option. When set to true, the operator removes specified attributes instead of keeping them. An allbut operator is also provided that has the same effect.

Implementation notes

Unlike SQL, this operator ALWAYS remove duplicates. There is no way, in Alf, to compute bags of tuples.