JIAKAOBO

LeetCode

venmo
wechat

感谢赞助!

  • ㊗️
  • 大家
  • offer
  • 多多！

Problem

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.

The query result format is in the following example.

Example 1:

Input: 
Variables table:
+------+-------+
| name | value |
+------+-------+
| x    | 66    |
| y    | 77    |
+------+-------+
Expressions table:
+--------------+----------+---------------+
| left_operand | operator | right_operand |
+--------------+----------+---------------+
| x            | >        | y             |
| x            | <        | y             |
| x            | =        | y             |
| y            | >        | x             |
| y            | <        | x             |
| x            | =        | x             |
+--------------+----------+---------------+
Output: 
+--------------+----------+---------------+-------+
| left_operand | operator | right_operand | value |
+--------------+----------+---------------+-------+
| x            | >        | y             | false |
| x            | <        | y             | true  |
| x            | =        | y             | false |
| y            | >        | x             | true  |
| y            | <        | x             | false |
| x            | =        | x             | true  |
+--------------+----------+---------------+-------+
Explanation: 
As shown, you need to find the value of each boolean expression in the table using the variables table.

Code

SELECT e.left_operand, e.operator, e.right_operand,
    (
        CASE
            WHEN e.operator = '<' AND v1.value < v2.value THEN 'true'
            WHEN e.operator = '=' AND v1.value = v2.value THEN 'true'
            WHEN e.operator = '>' AND v1.value > v2.value THEN 'true'
            ELSE 'false'
        END
    ) AS value
FROM Expressions e
JOIN Variables v1
ON e.left_operand = v1.name
JOIN Variables v2
ON e.right_operand = v2.name