Help to Find out the correct answer to the following query

Hi,

I have two tables named customer and salesorder.

In the customer table i have 1000 customers,Of which 900 customers have orders in the salesorder table.
i execute the following query to list all customer sthat have had at least one sale.


Select * from customer where customer.CustomerID in (Select Customer.CustomerID from salesorder)

you need to identify the result of the query? which result will the query return?

1) No rows
2) A Warning message
3) The 100 rows in the customer table
4 The 900 rows in the customer table with matching rows in the salesorder table.

I am thinking the answer is 4 but some are telling that the answer is 3.So can you plese tell me the correct answer with explanation.

Thank you