Leetcode SQL 1440. Evaluate Boolean Expression

Question

Table Variables:

Column Name	Type
name	varchar
value	int

name is the primary key for this table. This table contains the stored variables and their values.

Table Expressions:

Column Name	Type
left_operand	varchar
operator	enum
right_operand	varchar

(left_operand, operator, right_operand) is the primary key for this table. This table contains a boolean expression that should be evaluated. operator is an enum that takes one of the values ('<', '>', '=') The values of left_operand and right_operand are guaranteed to be in the Variables table.

Write an SQL query to evaluate the boolean expressions in Expressions table.

Return the result table in any order.

I am working on a SQL problem as shown in the above. I used MS SQL server and tried

SELECT
left_operand, operator, right_operand,
IIF(  
(left_values > right_values AND operator = '>') OR 
(left_values < right_values AND operator = '<' ) OR 
(left_values = right_values AND operator = '='), 'true', 'false') as 'value' 
FROM 
(SELECT *,
IIF(left_operand = 'x', (SELECT value FROM Variables WHERE name='x')
                      , (SELECT value FROM Variables WHERE name='y')) as left_values, 
IIF(right_operand = 'x', (SELECT value FROM Variables WHERE name='x')
                      , (SELECT value FROM Variables WHERE name='y')) as right_values
FROM Expressions) temp;

It works well on the test set but gets wrong when I submit it. I think my logic is correct, could anyone help take a look at it and let me know what my problem is?

Thank you!

We can't see your link unless we are subscribed to premium on that site, therefore not many people are going to be able to help you. — Charleh, Mar 05 '22 at 19:04
Even if the site was completely free and accessible, a question on SO must be self-contained. You can extract as little of the problem description as required to illustrate what you're struggling with, but it has to be more than nothing. — Jeroen Mostert, Mar 05 '22 at 19:14
@Charleh, my bad, I did not notice this is a premium problem. Let me post it. — alli666, Mar 05 '22 at 21:47
@JeroenMostert Thank you for letting me know. I just post the whole question. — alli666, Mar 05 '22 at 21:53

score 0 · Answer 1 · answered Mar 10 '22 at 13:38

It feels like your example code is a lot more complicated than it needs to be. That's probably why it's failing the check. In your FROM you're using sub-selects but really a simple inner join would work much simpler. Also, if there were variables other than X and Y it doesn't look like your example code would work. Here's my code that I wrote in Postgres (should work in any SQL though).

SELECT e.left_operand, l.value as left_val, e.operator, e.right_operand, r.value as right_val,
  CASE e.operator
  WHEN '<' THEN
      (l.value < r.value)
  WHEN '=' THEN
      (l.value = r.value)
  WHEN '>' THEN
      (l.value = r.value)
  END as eval
FROM 
    expression as e
JOIN
    variable as l on e.left_operand = l.name
JOIN
    variable as r on e.right_operand = r.name

Here's a screenshot of my output:

I also have a db-fiddle link for you to check out. https://www.db-fiddle.com/f/fdnJVSUQHS9Vep4uDSe5ZP/0

Leetcode SQL 1440. Evaluate Boolean Expression

1 Answers1