How to correctly compose a mysql query with a subquery to insert a new row?

Question

PHP

Need to insert a new row into the table, but one of the row's values ​​must be +1 to the maximum value of the "id_category" column in the specific user's table.
For example, if the table were not locked, then the query would be:

INSERT INTO category (
  name, 
  id_user, 
  id_category, 
  created
) VALUES (
  'новая категория', 
  1, 
  (SELECT MAX(id_category )+1 
  FROM category 
  WHERE id_user=1), 
  NOW()
)

How to make a correct request?

Answer 1

autoincrement? no, have not heard!

Answer 2

Went the other way. The question is irrelevant.