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# 1440. Evaluate Boolean Expression

<https://leetcode.com/problems/evaluate-boolean-expression>

## Description

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.

```

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             |
+--------------+----------+---------------+

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  |
+--------------+----------+---------------+-------+
As shown, you need find the value of each boolean exprssion in the table using the variables table.
```

## ac

```java
```