nested loop：
select empno, ename, dname, loc
from emp, dept
where emp.deptno = dept.deptno
for each row in (select empno, ename, deptno from emp) loop
for (select dname, loc from dept where deptno = outer.deptno) loop
If match then pass the row on to the next step
If inner join and no match then discard the row
If outer join and no match set inner column values to null
and pass the row on to the next step
end loop
end loop
sort-merge join :
select empno, ename, dname, loc
from emp, dept
where emp.deptno = dept.deptno
select empno, ename, deptno from emp order by deptno
compare the rowsets and return rows where deptno in both lists match
for an outer join, compare the rowsets and return all rows from the first list
setting column values for the other table to null
hash-join :
select empno, ename, dname, loc
from emp, dept
where emp.deptno = dept.deptno
determine the smaller row set, or in the case of an outer join,
use the outer joined table
select dname, loc, deptno from dept
hash the deptno column and build a hash table
select empno, ename, deptno from emp
hash the deptno column and probe the hash table
if match made, check bitmap to confirm row match
if no match made, discard the row
