# $1440. 计算布尔表达式的值
# https://leetcode-cn.com/problems/evaluate-boolean-expression/

# SQL架构
Create Table If Not Exists Variables (name varchar(3), value int);
Create Table If Not Exists Expressions (left_operand varchar(3), operator ENUM('>', '<', '='), right_operand varchar(3));
Truncate table Variables;
insert into Variables (name, value) values ('x', '66');
insert into Variables (name, value) values ('y', '77');
Truncate table Expressions;
insert into Expressions (left_operand, operator, right_operand) values ('x', '>', 'y');
insert into Expressions (left_operand, operator, right_operand) values ('x', '<', 'y');
insert into Expressions (left_operand, operator, right_operand) values ('x', '=', 'y');
insert into Expressions (left_operand, operator, right_operand) values ('y', '>', 'x');
insert into Expressions (left_operand, operator, right_operand) values ('y', '<', 'x');
insert into Expressions (left_operand, operator, right_operand) values ('x', '=', 'x');

# Write your MySQL query statement below
select
    e.left_operand as left_operand,
    e.operator as operator,
    e.right_operand as right_operand,
    case
        e.operator
        when '>' then if(v1.value > v2.value, 'true', 'false')
        when '<' then if(v1.value < v2.value, 'true', 'false')
        else if(v1.value = v2.value, 'true', 'false')
    end as value
from
    Expressions e
    left join Variables v1 on v1.name = e.left_operand
    left join Variables v2 on v2.name = e.right_operand;

# clean-up
drop table Variables;
drop table Expressions;