LeetCode:Database 98.计算布尔表达式的值
Posted Xiao Miao
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了LeetCode:Database 98.计算布尔表达式的值相关的知识,希望对你有一定的参考价值。
要求:写一个 SQL 查询, 以计算表 Expressions 中的布尔表达式。
表 Variables的结构:
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| name | varchar |
| value | int |
+---------------+---------+
name 是该表主键.
该表包含了存储的变量及其对应的值.
表 Expressions的结构:
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| left_operand | varchar |
| operator | enum |
| right_operand | varchar |
+---------------+---------+
(left_operand, operator, right_operand) 是该表主键.
该表包含了需要计算的布尔表达式.
operator 是枚举类型, 取值于('<', '>', '=')
left_operand 和 right_operand 的值保证存在于 Variables 表单中.
Variables 表:
+------+-------+
| name | value |
+------+-------+
| x | 66 |
| y | 77 |
+------+-------+
Expressions 表:
+--------------+----------+---------------+
| left_operand | operator | right_operand |
+--------------+----------+---------------+
| x | > | y |
| x | < | y |
| x | = | y |
| y | > | x |
| y | < | x |
| x | = | x |
+--------------+----------+---------------+
Result Table:
+--------------+----------+---------------+-------+
| left_operand | operator | right_operand | value |
+--------------+----------+---------------+-------+
| x | > | y | false |
| x | < | y | true |
| x | = | y | false |
| y | > | x | true |
| y | < | x | false |
| x | = | x | true |
+--------------+----------+---------------+-------+
如上所示, 你需要通过使用 Variables 表来找到 Expressions 表中的每一个布尔表达式的值.
SQL语句:
with d as(SELECT a.left_operand as l1,b.value as v1,a.operator as o1,a.right_operand as r1,c.value as v2
FROM expressions a
JOIN VARIABLES b
ON b.name=a.left_operand
JOIN VARIABLES c
ON c.name=a.right_operand)
select l1 as left_operand,o1 as operator,r1 as right_operand,if(o1=o2,'true','false') as value
from(
select l1,o1,r1,
case when v1>v2 then '>'
when v1=v2 then '=' else '<' end as o2
from d)e;
以上是关于LeetCode:Database 98.计算布尔表达式的值的主要内容,如果未能解决你的问题,请参考以下文章
Leetcode 178. Rank Scores (Database)
算法leetcode2331. 计算布尔二叉树的值(多语言实现)