MYSQL INSERT or UPDATE IF

Question

Been looking around the web for a while now and don\'t seem to be able to come across anything similar to what I want. I know it\'s something to do with the way I\'m writing

Answer 1

First, add a UNIQUE constraint on name, barcode, item, location and price.

ALTER TABLE  tableX
  ADD CONSTRAINT tableX_UQ
    UNIQUE (name, barcode, item, location, price) ;

Then you can use INSERT INTO ... ON DUPLICATE KEY UPDATE:

INSERT INTO tableX
  (name, barcode, item, location, price, quantity, date)
VALUES
  (?, ?, ?, ?, ?, ?, ?)
ON DUPLICATE KEY UPDATE
  quantity = CASE WHEN VALUES(date) > date
               THEN quantity + VALUES(quantity)        -- add quantity
               ELSE quantity                           -- or leave as it is
             END
, date = CASE WHEN VALUES(date) > date
               THEN VALUES(date) ;                     -- set date to new date
               ELSE date                               -- or leave as it is
             END 

---

REPLACE could also be used but there are differences in the behaviour (which especially matter if you have foreign keys). For details, see this question “INSERT IGNORE” vs “INSERT … ON DUPLICATE KEY UPDATE” and the answer by @Bill Kawin which discusses the differences between INSERT IGNORE, INSERT ... ON DUPLICATE KEY and REPLACE.