Oracle SQL correlated update

Question

I got three tables:

t1.columns: a,c
t2.columns: a,b
t3.columns: b,c,d

Now what I want is to update t1.c with t3.d. But I can\'t just update t1

Answer 1

If there is a one-to-many relationship between t1 and t2 or between t2 and t3 you will get many matches for each row in t1. If you know that all rows in t3 that belong to the same row in t1 have the same value in d, then you can use DISTINCT to remove (identical) duplicates.

UPDATE table1 t1
   SET t1.c = (select DISTINCT t3.d
               from table2 t2, table3 t3
               where t2.b = t3.b and t1.a = t2.a)                                  
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

Answer 2

You have a subquery that is returning more than one row. Use rownum to get just one row:

UPDATE table1 t1
   SET t1.c = (select d
               from (select t3.d
                     from table2 t2 join table3 t3
                          on t2.b = t3.b 
                     where t1.a = t2.a
                    ) t
                where rownum = 1
               )                                
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);

Answer 3

Sorry for the confusion but I solved it:

UPDATE table t1
SET t1.c = (select t3.d from table3 t3, table2 t2
                          where t1.a = t2.a and t2.b = t3.b and t3.c = t1.c)
 WHERE EXISTS ( SELECT 1 FROM table1 t1, table2 t2 WHERE t1.a = t2.a and t2.b = t3.b and t3.c = t1.c)

Answer 4

UPDATE table1 t1
   SET t1.c = (select MAX(t3.d)
               from table2 t2, table3 t3
               where t2.b = t3.b and t1.a = t2.a)                                  
 WHERE EXISTS ( SELECT 1 FROM table2 t2, table3 t3 WHERE t1.c = t3.c and t1.a = t2.a);