Value disappears when performing Update

Question

Hello.
Please advice about the following:
I am running Update statement for 2 columns, for one of them I am giving
the value by myself:
update Table1 f
set (f.Value_Field, f.name1)
=
(select '1', k.name
from Table2 k where k.field1=f.field1
and k.field2=f.field2);
Then I run other statement, with different logic:
update Table1 f
set (f.Value_Field, f.name2)
=
(select '2', k.name
from Table2 k where k.field1=f.field1
and k.field2 <> f.field2);
The second update is working fine, updating the relevant records.
But for some reason the value '1' of previous Update statement disappears... What can be the reason?
I am using COMMIT after each query...
Thanks!

Answer 1

To be really explicit about what everyone is saying, your first statement updates every row in table1. If there is a corresponding row in table 2 based on a match of field1 and field2, it will set the values of value_field and name1 to the result of the sub-query. If there is no matching row, then both value_field and name1 will be set to NULL.
Your second query work similarly, seting value_field and name1 to NULL if there is no matching row. Minimally, your second update needs to be more like:
UPDATE table1 f
SET (f.value_field, f.name2) = (SELECT '2', k.name
                                FROM table2 k
                                WHERE k.field1 = f.field1 and
                                      k.field2 <> f.field2)
WHERE EXISTS (SELECT 1
              FROM table2 k
              WHERE k.field1 = f.field1 and
                    k.field2 <> f.field2);and probably your first needs to be:
UPDATE table1 f
SET (f.value_field, f.name1) = (SELECT '1', k.name
                                FROM table2 k
                                WHERE k.field1 = f.field1 and
                                      k.field2 = f.field2)
WHERE EXISTS (SELECT 1
              FROM table2 k
              WHERE k.field1 = f.field1 and
                    k.field2 = f.field2);HTH
John