How to get the maximum depth of a tree?

Question

MySQL

Please help with requests. There is a group tree table: id, name, uplevel. Accordingly, the uplevel contains the id of the parent group. Let's say in group 1 there is 1 more nested subgroup, in the second the depth is 5, and in the third, only 2. How to find out that the maximum depth is 5?

Answer 1

At such representation of a tree - only to count. Get a list of id's of all groups that do not have a parent, then until the resulting list is empty, get a list of all groups whose parent groups are in the current list. Well, count how many of these levels are passed.