How can I return only objects where the sub-object exists?

Question

I'm doing this query

Select id, name, (select quantity, PriceBookEntry.Name from OpportunityLineItems where quantity  != NULL)  from Opportunity where StageName = 'Closed Won'

And it'll return a bunch of Opportunities, but for some of them, OpportunityLineItems will be null.

How can I only return the Opportunities that have OpportunityLineItems?

Doing and OpportunityLineItems != NULL makes the query crash with

Invalid Field [object Object]: where StageName = 'Closed Won' and OpportunityLineItems != NULL ^ ERROR at Row:1:Column:158 No such column 'OpportunityLineItems' on entity 'Opportunity'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.

Answer 1

How about filtering if the Opportunity ID is in the OLI table

    Select id, name, (select quantity, PriceBookEntry.Name from OpportunityLineItems where quantity != NULL) from Opportunity where StageName = 'Closed Won' AND ID in (select OpportunityID from OpportunityLineItem)

Answer 2

You can query the OpportunityLineItem object limiting the set returned by checking the parent ID like this:

select Quantity, PriceBookEntry.Name, Opportunity.Id, Opportunity.Name
from OpportunityLineItem
where Quantity != null
and OpportunityId in (select Id from Opportunity where StageName = 'Closed Won')

That automatically eliminates Opportunity objects that have no OpportunityLineItems.