Update statement - no data found issue

Question

Hello,
I have two tables (temp_A and temp_B), they both have two columns (col_1 and col_2)
The following is the data in temp_A:
(1,'A'), (2,'B'), (3,'C'), (4, 'D'), (5, 'E')
The following is the data in temp_B:
(1,'Z'), (2,'Y'), (3,'X'), (4, 'W')
When I run the following query:
update temp_A set col_2 = (select col_2 from temp_B where temp_A.col_1 = temp_B.col_1);
The outcome of temp_A is
(1,'Z'), (2,'Y'), (3,'X'), (4, 'W'), (5,'')
Is there any way that I can get this update statement to skip the row if no data is found instead of setting it to null (because the pairing does not exist in temp_B and thus (5,'') is misleading).
Thanks in advance,
Ivan

Answer 1

Try this -
MERGE INTO temp_a a
   USING (SELECT b.col_1, b.col_2
            FROM temp_b b) b1
   ON (a.col_1 = b1.col_1)
   WHEN MATCHED THEN
      UPDATE
         SET a.col_2 = b1.col_2;Tested -
SQL> select * from temp_a;
     COL_1 CO
         1 A
         2 B
         3 C
         4 D
         5 E
Elapsed: 00:00:00.00
SQL>
SQL> select * from temp_b;
     COL_1 CO
         1 Z
         2 Y
         3 X
         4 W
SQL> MERGE INTO temp_a a
  2     USING (SELECT b.col_1, b.col_2
  3              FROM temp_b b) b1
  4     ON (a.col_1 = b1.col_1)
  5     WHEN MATCHED THEN
  6        UPDATE
  7           SET a.col_2 = b1.col_2
  8        ;
4 rows merged.
SQL> select * from temp_a;
     COL_1 CO
         1 Z
         2 Y
         3 X
         4 W
         5 EEdited by: Sri on May 26, 2011 1:41 PM
Edited by: Sri on May 26, 2011 1:49 PM