Types and Domains / Chapter 233
available for the relations in question─they can be restricted, projected, joined, and so on. By contrast, if we were to use general sets instead of relations, then we would need to introduce new operators (set union, set intersection, and so on) for dealing with those sets ... Much better to get as much mileage as we can out of the operators we already have!
7 The individual elements in an SQL multiset don’t have to be rows but can be values of any available SQL type─for example, integers. The same goes for arrays as well.
34Chapter 2 / Types and Domains
Note also that qualifier named: Types with different names are different types.
that every value v that can legally be assigned to V is in turn of type T.
Every expression denotes some value and is therefore of some type: namely, the type of the value in question, which is to say the type of the value returned by the outermost operator in the expression (where by “outermost” I mean the operator that’s executed last). For example, the type of the expression