Wrapping and unwrapping in SQL
Operators WRAP and UNWRAP in connection with attributes whose declared types are tuple types. Example shows how extension and projection can be used to replace a given set of attribute values in each tuple of a given relation by a single tuple consisting of those values; the next example then illustrates the use of WRAP as a convenient shorthand for the same purpose (on the admittedly rare occasions on which it is likely to arise in practice).