mysql cross check tag query

I have two tables one with Items and one with tags I want to find every item in the items table that has the tag "foo" but not the tag bar so if I where going to select all items that have the tag "foo" my query would be

 SELECT * FROM items i INNER JOIN tags t on i.id= t.id WHERE tag= "foo"

and I开发者_开发百科 get all items with tags of "foo" so how do I subquery to take out all the items that are also tagged "bar"

EDIT based on Matthew Coxa solution provided bellow I cam up with this if anyone sees any flaw with this please let me know

      SELECT * FROM items i INNER JOIN 
        tags t ON t.item_id=i.id 
        WHERE tag = 'foo' 
        AND NOT EXISTS (
            SELECT * FROM tags tt WHERE t.item_id = tt.item_id AND tag = 'bar'
        )

SELECT *
FROM items i

INNER JOIN tags t
ON i.id = t.id

WHERE t.tag = "foo" AND NOT EXISTS (
    SELECT *
    FROM items ii

    INNER JOIN tags tt
    ON ii.id = tt.id 

    WHERE tt.tag = "bar" AND tt.id = t.id)

select
    *
from
    items i
where
    exists (select * from tags t where t.id = i.id and t.tag = "foo")
and
    not exists (select * from tags t where t.id = i.id and t.tag = "bar")

or

;with ItemTagCount as (
    select
        t.id,
        sum(case t.tag when "foo" then 1 else 0 end) as FooCount,
        sum(case t.tag when "bar" then 1 else 0 end) as BarCount
    from
        tags t
    group by
        t.id
)
select
    i.*
from
    items i
inner join
    ItemTagCount itc on itc.id = i.id
where
    itc.FooCount >= 1 and itc.BarCount = 0