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1440. Evaluate Boolean Expression

中文文档

Description

Table Variables:

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| name          | varchar |
| value         | int     |
+---------------+---------+
In SQL, 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 |
+---------------+---------+
In SQL, (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.

 

Evaluate the boolean expressions in Expressions table.

Return the result table in any order.

The 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.

Solutions

SQL

# Write your MySQL query statement below
SELECT
    left_operand,
    operator,
    right_operand,
    CASE
        WHEN (
            (e.operator = '=' AND v1.value = v2.value)
            OR (e.operator = '>' AND v1.value > v2.value)
            OR (e.operator = '<' AND v1.value < v2.value)
        ) THEN 'true'
        ELSE 'false'
    END AS value
FROM
    Expressions AS e
    LEFT JOIN Variables AS v1 ON e.left_operand = v1.name
    LEFT JOIN Variables AS v2 ON e.right_operand = v2.name;