DECLARE
  stmt    varchar2(1000);
  c_rec   all_constraints%ROWTYPE;

BEGIN

  /* Remove foreign keys */
  FOR c_rec IN
    (select *
     from all_constraints
     where owner='xxx'
     and table_name like 'yyy%'
     and constraint_type = 'R')
  LOOP
    stmt :=  ' ALTER TABLE ' || c_rec.owner ||
             '.' || c_rec.table_name ||
             ' DROP CONSTRAINT ' || c_rec.constraint_name;
    execute immediate stmt;
  END LOOP;