Unwrap

Inverse of wrap

Signature

unwrap(operand: Relation, tva: AttrName) -> Relation

Examples

unwrap(wrap(suppliers, [:city, :status], :extra), :extra)

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Description

Computes the relation obtained by unwrapping a tuple-valued attribute tva. Unwrapping of tva on an input tuple t consists in removing tva from t and extending the result with tva's own attributes:

Tuple(x: 1, tva: Tuple(y: 2, z: 3)) -> Tuple(x: 1, y: 2, z: 3)

tva must be a tuple-valued attribute. It should not itself contain any attribute whose name clashes with an attribute of operand. In the examples above, tva may not contain an attribute called x.

Implementation notes

This operator does not compile to SQL so far. Contributions are welcome to provide it with a SQL compilation for SQL DBMSs that support this kind of feature (e.g. PostgreSQL with JSON data type)