Find all airlines that have flights from both airports 'APG' and 'CVO'.
create table airlines (airline varchar, uid varchar, PRIMARY KEY (airline)); create table flights (airline varchar, sourceairport varchar, PRIMARY KEY (airline))
select t1.airline from airlines as t1 join flights as t2 on t1.uid = t2.airline where t2.sourceairport = "apg" intersect select t1.airline from airlines as t1 join flights as t2 on t1.uid = t2.airline where t2.sourceairport = "cvo"