Question

Is there a way to make a value increment with every insert if having multiple inserts? (I dont speak of the primary key that autoincrements)

Lets say I have a structure like this:

|ID_PRODUCT|ID_CATEGORY|NAME|POSITION|

So I have individual product ids, each produt belongs to a category and has a different position in this category. I want to do something like this:

INSERT INTO products
( SELECT id_product, id_category, name, MY_POSITION++
  FROM db2.products WHERE id_category = xxx )

So there should be a variable MY_POSITION that starts with 1 and increments every insert.

It would be really easy to do this all just with a scripting-language like php or python, but I want to get better with SQL 🙂

Answer 1

Yes: Use a user defined variable:

SET @position := 0; -- Define a variable
INSERT INTO products
SELECT id_product, id_category, name, (@position := @position + 1)
FROM db2.products
WHERE id_category = xxx;

The result of increment to @position is the value used for the insert.

---

Edit:

You can skip the declaration of the variable by handling the initial value in-line:

...
SELECT ..., (@position := ifnull(@position, 0) + 1)
...

This can be particularly handy when executing the query using a driver that does not allow multiple commands (separated by semicolons).