Best way to do this: Insert if exists, otherwise update

Question

Hi Everyone,
I'm trying to write a PL/SQL procedure to check whether a row is in Table A. If the row exists, then update. I was using a
SELECT Count(1) into countVariable FROM Table A where pri_key = data;
but was recommended otherwise since a count() does a tablescan. Intead, I was suggested to use BEGIN / EXCEPTION WHEN NO_DATA_FOUND.
You see, I'm not really an Oracle person, but to me using an exception for logic flow control is a no no. Is this the proper way of doing things?
What about if I did something like:
SELECT 1 into countVariable FROM Table A where pri_key = data;
Not sure....
Thanks!
dfa_geko

Answer 1

Assuming you're on 9i or later, you're better off using MERGE
SCOTT @ nx102 Local> create table a( pk number primary key, val varchar2(10) );
Table created.
Elapsed: 00:00:00.36
SCOTT @ nx102 Local> create table b( pk number primary key, val varchar2(10) );
Table created.
Elapsed: 00:00:00.48
SCOTT @ nx102 Local> insert into a values( 1, 'abc' );
1 row created.
Elapsed: 00:00:00.00
SCOTT @ nx102 Local> insert into a values( 2, 'def' );
1 row created.
Elapsed: 00:00:00.00
SCOTT @ nx102 Local> insert into b values( 2, 'ghi' );
1 row created.
Elapsed: 00:00:00.01
SCOTT @ nx102 Local> commit;
Commit complete.
Elapsed: 00:00:00.00
  1  MERGE INTO b USING a ON (a.pk = b.pk)
  2  WHEN MATCHED THEN UPDATE SET b.val = a.val
  3* WHEN NOT MATCHED THEN INSERT (pk, val) VALUES( a.pk, a.val )
SCOTT @ nx102 Local> /
2 rows merged.
Elapsed: 00:00:00.11
SCOTT @ nx102 Local> select * from a;
        PK VAL
         1 abc
         2 def
Elapsed: 00:00:00.01
SCOTT @ nx102 Local> select * from b;
        PK VAL
         2 def
         1 abc
Elapsed: 00:00:00.00
SCOTT @ nx102 Local> Justin