SELECT
    n,
    CASE
        WHEN p IS NULL THEN 'Root'
        WHEN n IN (SELECT DISTINCT p FROM bst) THEN 'Inner'
        WHEN n NOT IN (SELECT DISTINCT p FROM bst WHERE p IS NOT NULL) THEN 'Leaf'
    END AS conditionTable
FROM bst
ORDER BY n;

-- Why condition for 'Leaf' must have WHERE p IS NOT NULL b/c NOT IN is entangle with NULL. If you're not write WHERE clause, the result are returned with NULL value

-- On the other hand why condition for 'Inner' no need to have WHERE clause like 'Leaf' b/c IN is not entangle with NULL. It disregard NULL