. . : () ; .
, , , , : , . , .
1. (projection, "π") ( ), R. , .
2. (selection, "σ") , , , .
3. (cartesian product, "×") .
4. (union, " U") R S, , .
5. (set difference, "") (RS), R, S.
6. (intersection, "∩") R S, , .
7. (join, " ") R S. (, ). , . , . , .
, , .
8. (division, "/") R S. R {r1,r2,...,ri,...,rn}, S {r1,r2,...,ri}. {ri+1,...,rn}. , S R.