To help you understand SQL I should point out that your version would work (assuming only 1 school per person) if you just left the friends out of the FROMs for the sub-selects:-
select frienda, friendb from friends where (select schools.school from schools as schoolsa where friends.frienda = schools.person) = (select schools.school from schools as schoolsb where friends.friendb = schools.person); This is because the only thing that the sub-selects need to know from friends is the person to retrieve for, and that comes from the WHERE clauses. Although what Josh said is correct, and his is a better solution as it can cope with the 2+ schools per person problem. Josh Berkus wrote: > snip... > Mike, > > > select frienda, friendb from friends where (select > > schools.school from friends,schools where friends.frienda = > > schools.person) = (select schools.school from friends,schools where > > friends.friendb = schools.person); > > Too complicated. You need to learn how to use JOINS and table aliases > (or find yourself some friends who know SQL!): > > SELECT friends.frienda, friends.friendb > FROM friends JOIN schools schoola ON friends.frienda = schoola.person > JOIN schools schoolb ON friends.friendb = schoolb.person > WHERE schoola.school = schoolb.school > > and, if it's possible that any particular person went to more than one > school, add: > > GROUP BY frienda, friendb > > Simple, neh? > > -Josh snip.. -- This is the identity that I use for NewsGroups. Email to this will just sit there. If you wish to email me replace the domain with knightpiesold . co . uk (no spaces). ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
