I was solving a problem in Hackerrank, and I tried the following snippet for my solution:
SELECT N AS VALUE,
CASE
WHEN P IS NULL THEN "Root"
WHEN N NOT IN (SELECT P FROM BST) THEN "Leaf"
ELSE "Inner"
END
AS TYPE FROM BST ORDER BY N ASC;
But this proved to be not correct. Then I inverted the second case and the last, then it worked out. It looks as follows:
SELECT N AS VALUE,
CASE
WHEN P IS NULL THEN "Root"
WHEN N IN (SELECT P FROM BST) THEN "Inner"
ELSE "Leaf"
END
AS TYPE FROM BST ORDER BY N ASC;
Then I checked to see whether it is supported or not.
According to the link above, it seems it is a supported operation. So what's wrong with the first snippet?
