Question

I have a table T1 with fields f1 and f2 and a table T2 with fields f3 and f4.

Let ‘s have some dummy values :

T1: (1,1) (2,3) (3,3) (4,3) (5,1)
T2: (1,1) (1,2) (3,1) (3,3)

We can think of f2 and f3 as defining the same thing, a bridge between T1 and T2. I would like to retrieve every f1 that is not associated with a f4 value of 2 . So my expected output would be :

(2),(3),(4) as at the 1 and 5 F1 value F2=F3=1 has f4=2 on T2.

How can I achieve this ?

Edit 2 : I forgot to mention that T1 is derived from a long process and expected to be a small table whereas T2 is massive, and impossible to operate on without indexes

Answer 1

Because f2 and f3 are the same thing, you join between the two fields.

select f1 
from t1 
    left join t2 
        on t1.f2 = t2.f3 
        and t2.f4=2
where f3 is null