SQL是否存在更新数量

Question

What I'm trying to achieve is a single form where user with a handheld barcode reader read the barcode and the page on each read send a SQL command to record the number of product scanned.

I have a database named packinglist and a table named list with two columns barcode and quantity.

I have this string on the page:

INSERT INTO `gpbeticlm`.`packinglist` (barcode,quantity) VALUES (':field',1) ON DUPLICATE KEY UPDATE quantity=VALUES(quantity);

The first time I read a barcode it is inserted correctly in the database with quantity 1, but the second time I read the same barcode instead of having quantity 2 it doesn't update the database and remain 1, so I try to read another barcode and it doesn't do nothing the database keep 1 row with quantity 1.

Answer 1

If the barcode is the primary key of the table, you could use the INSERT...ON DUPLICATE KEY UPDATE construct

You can find more information about this construct here

I'll try to clarify a bit.

You're doing ON DUPLICATE KEY UPDATE quantity=VALUES(quantity); , which takes the inserted value (which is 1 ) as the value to write in the updated field. So this will always be 1 instead of the incremented value.

You could rewrite this construct as mentioned in the beforementioned link to something like this

ON DUPLICATE KEY UPDATE quantity=quantity + 1