Please help on SQL

Hi Gurus,

I am looking for the efficient way to construct SQL statement for following

requirement, and I seem to be running out of ideas.

following is the table and some sample data,

Table foo :     Column a        Column b       Column c       Column d
                	111             222             0000            	999
                	111             223             0000            	4000
                	111             223             4001            	5000
                	222             333             3333            	4444
                	333             444             0000            	3000
                	333             444             3001            	5000

Basically, I want to retrieve column A and Column B from all those records of
table foo where there is more than one entry for each column A and column B

pair. Having said that the result of the mentioned query should return following data from the table foo.

        a       b
        --      --
        111     223
        333     444

 In other words, I want something like this,
(Following is **NOT** a SQL statement, I just used to convey the idea)

Select pp.a, pp.b from foo pp where
(select count(*) from foo yy where yy.a = pp.a and yy.b = pp.b ) > 1;

Thanks in advance,

-- 
Shetal Sheth
sheths_at_bobcat.ent.ohiou.edu