f# - Query expression with join on multi part key and nullables -

f# - Query expression with join on multi part key and nullables -

consider next 2 tables, 3 columns each:

table 1:

a integer not null, b integer not null, c integer not null

table 2:

d integer not null, e integer, f integer not null

i'm trying write query look joins 2 tables on 2 part, composite key: (b, c) = (e, f).

i know if column e not nullable write:

query { r1 in c.table1 bring together r2 in c.table2 on ((r1.b, r1.c) = (r2.e, r2.f)) . . }

but how do if column e nullable column b in not?

f# f#-3.0 query-expressions