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.

Answer 2

You could use the replace syntax in mysql.

But that would work only with a unique index on... the fields needing to be unique.

So you'd have to create a unique index like that :

alter <yourtable> add unique index(name, barcode, item, location, price);

then your insert/update syntax would become

replace into <yourtable> (name, barcode, item, quantity, location, price, date)
 VALUES('name1', 'barcode1', 2, 'location1', 12.0, '25/12/2012');

EDIT

Example of stored procedure (simplified and untested) :

DELIMITER &&
DROP PROCEDURE IF EXISTS MyBase.UpdateOrInsert $$
CREATE PROCEDURE MyBase.UpdateOrInsert
(
  IN _name VARCHAR(10),
  IN _barcode VARCHAR(50),
  IN _quantity INTEGER
  IN _date DATE
)

DECLARE existingDate DATE default NULL;
BEGIN

SELECT date 
INTO existingDate
FROM <yourTable> where name = _name and barcode = _barcode;

if (existingDate IS NULL) then
   insert into <yourtable> (name, barcode, quantity, date) VALUES(_name, _barcode, _qantity, _date);
else
  if (existingDate < _date) then
     update <yourtable> 
     set quantity = _quantity,
       date = _date
     where name = _name
     and   barcode = _barcode;
  end if;
end if;
END &&

Answer 3

Thanks to all the help from those above the solution I found in the end was very close to both. Find it below:

INSERT INTO `stock`
    (name, barcode, item, quantity, location, price, date)  
VALUES
    (?,?,?,?,?,?,?)                         
ON DUPLICATE KEY UPDATE
     quantity = CASE WHEN 
                VALUES(date) < $date
                THEN quantity + $quantity
                ELSE quantity 
                END,
    date = CASE WHEN 
                VALUES(date) < $date
                THEN VALUES(date)
                ELSE $date
                END