MySQL UPSERT without ON DUPLICATE KEY

Question

I want a UPSERT (UPDATE if exists, else insert) on a MySQL table with these fields:

CREATE TABLE item (
  uid int(11) NOT NULL AUTO_INCREMENT,
  timestamp int(11) NOT NULL DEFAULT '0',
  category1 int(11) NOT NULL DEFAULT '0',
  category2 int(11) NOT NULL DEFAULT '0',
  counter int(11) NOT NULL DEFAULT '1',
  PRIMARY KEY (`uid`)
)

This table is already in productive use, and the combination of (timestamp,category1,category2) is for my INSERT unique, but not for the whole table content. That's the reason why I can't use the "ON DUPLICATE KEY" feature.

For clarification about the UNIQUE problem: If category1=9 then this is my insert, and (timestamp,category1,category2) is unique. But the table is in productive use, and if category1=1,2 then (timestamp,category1,category2) is not unique. As far as I know I can't add a UNIQUE key, as it would create problems with the categories 1+2.

What I need is something like this:

 IF (timestamp,category1,category2) exists 
     counter=existingCount + newCount
 ELSE 
     insert new record

I use PHP and MySQL, so any combination of both languages is fine.

What I tried already, but takes too much time is:

• Single PHP SELECT statement, then UPDATE or INSERT
• INSERT everything then UPDATE and DELETE duplicate rows

Thanks to answers I created now this Stored Procedure, syntax is OK but procedure is not working:

DROP PROCEDURE IF EXISTS myUpsert;
DELIMITER |
CREATE PROCEDURE myUpsert (IN v_timestamp INT, IN v_category1 INT, IN v_category2 INT, IN v_counter INT)        
BEGIN
  DECLARE existingCounter INT;
  SELECT COUNT(counter) AS existingCounter from item 
  WHERE timestamp =v_timestamp  AND category1=v_category1 AND category2=v_category2;

  IF existingCounter=0 THEN
    INSERT INTO item (timestamp,category1,category2,counter) 
    VALUES (v_timestamp,v_category1,v_category2,v_counter);
  ELSE
    UPDATE item SET count=v_counter+existingCounter
    WHERE timestamp=v_timestamp AND category1=v_category1 AND category2=v_category2;
  END IF;
END
|
DELIMITER ;

Answer 1

DROP PROCEDURE IF EXISTS myUpsert;
DELIMITER |
CREATE PROCEDURE myUpsert (IN v_timestamp INT, IN v_category1 INT, IN v_category2 INT, IN v_counter INT)        
BEGIN
DECLARE existingCounter INT;
  SET existingCounter = (SELECT COUNT(counter) from item 
  WHERE timestamp =v_timestamp  AND category1=v_category1 AND category2=v_category2);

IF existingCounter=0 THEN
 INSERT INTO item (timestamp,category1,category2,counter) 
 VALUES (v_timestamp,v_category1,v_category2,v_counter);
ELSE
 UPDATE item SET count=v_counter+existingCounter
 WHERE timestamp=v_timestamp AND category1=v_category1 AND category2=v_category2;
 END IF;
END
|
DELIMITER ;

Answer 2

I suggest adding a unique index for those three columns:

ALTER TABLE item ADD UNIQUE (timestamp, category1, category2)