INSERT ON DUPLICATE KEY UPDATE with last_insert_id() - mysql

Question

im trying to create a function
CREATE FUNCTION `func`(param1 INT, param2 INT, param3 TEXT) RETURNS int(11)
BEGIN
INSERT INTO `table1` (`column1`, `column2`, `column3` )
VALUES (param1, param2, param3)
ON DUPLICATE KEY
UPDATE `time_stamp` = UNIX_TIMESTAMP();
RETURN last_insert_id();
END
this would insert into a table a row if it doesn't exist but otherwise update it.
Notice that i returned last_insert_id() which would be correct if the function would insert otherwise would be unpredictable if it updates.
I know the alternative to solving this is using separate SELECTS and identify if it exists; if it exists retrieve the id and update using that id; otherwise just do a plain INSERT.
Now my question: Is there any alternative to doing 2 sql statements as opposed to what i'm doing now?
EDIT 1
Addendum:
there is an auto incremented index.
All of the values to be inserted are unique
I'd rather not alter the index since it is being referred in another table..

Answer 1

If a table contains an AUTO_INCREMENT column and INSERT ... UPDATE inserts a row, the LAST_INSERT_ID() function returns the AUTO_INCREMENT value. If the statement updates a row instead, LAST_INSERT_ID() is not meaningful. However, you can work around this by using LAST_INSERT_ID(expr). Suppose that id is the AUTO_INCREMENT column. To make LAST_INSERT_ID() meaningful for updates, insert rows as follows:
INSERT INTO table (a, b, c) VALUES (1, 2, 3)
ON DUPLICATE KEY UPDATE id = LAST_INSERT_ID(id), c = 3;
Found it on this link. I've never tried it though, but it might help you.
EDIT 1
You might want to check out REPLACE:
REPLACE INTO table1 (column1, column2, column3) VALUES (param1, param2, param3);
This should work for tables with correct PRIMARY KEY/UNIQUE INDEX.
In the end, you'll just have to stick with:
IF (VALUES EXISTS ON TABLE ...)
UPDATE ...
SELECT Id;
ELSE
INSERT ...
RETURN last_insert_id();
END IF

Answer 2

Just in case anyone shows up here from Google, I ran into a problem where ON DUPLICATE KEY UPDATE kept triggering the same wrong value.
When inserting a user with only a first name and last name, it didn't AUTO_INCREMENT the primary key. The reason is we have a users table with a unique constraint on the username, but it has a default value of ''. So when you insert a user without a username, it triggers it to update the duplicate value of that username, and that random account kept getting returned as the correct one.
The solution is to make sure that only NULL is the default value for a unique key in a table that also has a separate auto-increment primary key, or that you do generate a unique value for the unique constraint.