At the basis of relational data bases is the relational algebra, an algebra on sets of tuples (“relations”) defining six
operators:
- unary select – select tuples matching to some condition
- unary project – make a set of sub-tuples of all tuples (i.e., have less
columns)
- unary rename – change the name of a relation (this is a rather technical operation)
- binary cartesian product –
the usual cartesian product, except that the tuples are concatenated rather than just put into a pair; this, of course,
is not usually actually computed but rather used as a formal step.
- binary union – simple union of sets. This is only
defined for “compatible” relations; the technical points don’t matter here
- binary set difference as for union; you could
have used intersection and complementing as well, but complementing is harder to specify in the context of relational
algebra
Good News: You don’t need to know any of this. But it’s reassuring to know that there’s a solid theory behind all of
this.