Operation in relational algebra or in an RDBMS to partition relations. The inverse of a Cartesian product (CROSS JOIN).
E.F. Codd identified eight relational algebra operators in his defining paper "A Relational Model of Data for Large Shared Data Banks". Division is the least known and probably most complex of them. It is the inverse operation of a Cartesian product (CROSS JOIN in SQL).
It means partitioning a (bigger) table with rows from another (smaller) table. For requirements like:
"Find tuples that combine a particular value in one attribute with several values in another attribute."
A practical example:
"Find all clubs where Sue and John and James are members."
