for only a join field, with a simple condition:

CREATE CURSOR CC1 (A I,B I,C I)
INSERT INTO CC1 VALUES (1,1,0)
INSERT INTO CC1 VALUES (2,1,0)
INSERT INTO CC1 VALUES (2,1,0)
INSERT INTO CC1 VALUES (3,1,0)
CREATE CURSOR CC2 (A I,C I)
INSERT INTO CC2 VALUES (1,11)
INSERT INTO CC2 VALUES (2,22)
INSERT INTO CC2 VALUES (3,33)
UPDATE CC1 SET C=LOOKUP(CC2.C,A,CC2.A)
SELECT CC1
BROWSE 

If CC2.A is indexed LOOKUP use the index, otherwise it scan, and return the first CC2.C

Fabio