How many 'United Airlines' flights depart from Airport 'AHD'?
create table flights (airline varchar, sourceairport varchar, PRIMARY KEY (airline)); create table airlines (uid varchar, airline varchar, PRIMARY KEY (uid))
select count(*) from airlines as t1 join flights as t2 on t2.airline = t1.uid where t1.airline = "united airlines" and t2.sourceairport = "ahd"