Update statement with joins

Question

Hi all, consider the tables and data below
CREATE TABLE table1 (id NUMBER, a NUMBER, b NUMBER) ;
CREATE TABLE table2 (id NUMBER, c NUMBER, d NUMBER);
INSERT INTO table1 VALUES(111,2,0);
INSERT INTO table1 VALUES(111,1,2);
INSERT INTO table1 VALUES(111,1,3);
INSERT INTO table1 VALUES(222,1,3);
INSERT INTO table2 VALUES(111,5,8);
INSERT INTO table2 VALUES(222,6,7);
what i want to do is write a UPDATE STATEMENT that joins the two tables BY id
and update table1 rows. i want to include the following CASE statement
UPDATE COLUMN a intable1 according to this logic
case
WHEN b >0
THEN nvl(c,b)
ELSE
d
END
so table1 after the update should look like this
id    a   b
111   8   0
111   5   2
111   5   3
222   6   3can somebody help write a update statement that update table1 according to case statement and joins both tables to get the values necessary? thanks

Answer 1

Hooray for sample tables!
SQL> alter table table2 add constraint table2_pk primary key (id);
Table altered.
SQL> update
  2     (select t1.a
  3            ,case when t1.b > 0 then nvl(t2.c, t1.b)
  4                  else t2.d
  5             end new_value
  6      from   table1 t1
  7      join   table2 t2
  8             on t1.id = t2.id
  9     )
10  set a = new_value;
4 rows updated.
SQL> select * from table1;
                  ID                    A                    B
                 111                    8                    0
                 111                    5                    2
                 111                    5                    3
                 222                    6                    3