SQL Query

Hello,
have got a query in sql

members contribution certain money at different periods...after some time they withdraw that money which was invested.

i need to sum up the members and exlcude the members which show zero values.

example

member id investment withdrawal
1 1000
2 2000
3 500
1 1000
2 1000
4 1000
5 200

the query should add all the investment by member id and substract all the withdrawals...and only those greater than zero should be displayed.
per the above table we the query result shoudl display
2 1000
3 500
4 1000
5 200

thanks alot...