Question

I need two id columns in the same table that create unique values upon insert. Since MySQL allows only one column to auto-increment, I need to do something like max(id)+1 for the other column.

Here’s the SQL I expected to work:

INSERT INTO invoices (invoiceid)
VALUES ((SELECT MAX(invoiceid)+1 FROM invoices))

The select statement works independently, but within my INSERT, it’s not allowed. I get the error : You can’t specify target table ‘invoices’ for update in FROM clause

Answer 1

You want to use INSERT INTO .... SELECT FROM instead of INSERT INTO...VALUES():

INSERT INTO invoices (invoiceid)
SELECT MAX(invoiceid)+1 
FROM invoices

My question for you would be why are you not use an AUTO INCREMENT field to generate the invoiceid value? That is what it is for, then you will not have to create this when inserting data.