What is faster?
the Merge statement
MERGE INTO table_name
USING dual
ON (row_id = 'some_id')
WHEN MATCHED THEN
UPDATE SET col_name = 'some_val'
WHEN NOT MATCHED THEN
INSERT (row_id, col_name)
VALUES ('some_id', 'some_val')
or
querying a select statement then using an update or insert statement.
SELECT * FROM table_name where row_id = 'some_id'
if rowCount == 0
INSERT INTO table_name (row_id,col_name) VALUES ('some_id','some_val')
else
UPDATE table_name SET col_name='some_val' WHERE row_id='some_id'
The rule of thumb is, if you can do it in one SQL, it'll generally perform better than doing it in multiple SQL statements.
I'd go with the MERGE if it does the job.
Also - another suggestion: you can avoid repeating data in your statement, e.g.:
MERGE INTO table
USING (SELECT 'some_id' AS newid,
'some_val' AS newval
FROM dual)
ON (rowid = newid)
WHEN MATCHED THEN
UPDATE SET colname = newval
WHEN NOT MATCHED THEN
INSERT (rowid, colname)
VALUES (newid, newval)