Hey i have the following query
There are two tables
		Couples (WifeName, HusbandName)
		Cities(Name, City)

First table contains couples and each name is unique
Second table contains name of person and city where the person likes
to travel to (Each person can have multiple correspondent cities)

a. Find couples that like to travel to the same city (in format
WifeName, HusbandName, City)
b. Find couples that do not have the same city

All sql people give it a shot, sorry guys only have $2.50 to spare.

Your problem statements are a tad ambiguous.  The wordings as I am
interpreting are:

a. Find all cities where both the husband and wife like to travel.

You say find all couples, so it sounds like you want unique couples. 
It is possible, however, that a sinlge couple have more than one city
in common.  Then your answer format asks for city name, which sounds
like you want each city, even if the couple repeats for multiple
cities.

b. Find all couples such that the wife and husband do not have any
cities in common.

SQL

a.

select distinct
	WifeName,
	HusbandName,
	hc.City
from	Couples c
join	Cities hc on (c.HusbandName = hc.Name)
join	Cities wc on (c.WifeName = wc.Name)
where	hc.City = wc.City

b.

select	WifeName,
	HusbandName
from	Couples
where	WifeName not in (	select distinct
					WifeName
				from	Couples c
				join	Cities hc on (c.HusbandName = hc.Name)
				join	Cities wc on (c.WifeName = wc.Name)
				where	hc.City = wc.City )