Evaluate Boolean Expression - Problem
You are given two tables: Variables and Expressions.
The Variables table stores variable names and their integer values. The Expressions table contains boolean expressions with left operand, operator, and right operand.
Your task is to evaluate each boolean expression by looking up the variable values and applying the given operator ('<', '>', or '=').
Return the result of each boolean expression evaluation in any order.
Table Schema
Variables
| Column Name | Type | Description |
|---|---|---|
name
PK
|
varchar | Variable name (primary key) |
value
|
int | Integer value of the variable |
Primary Key: name
Expressions
| Column Name | Type | Description |
|---|---|---|
left_operand
PK
|
varchar | Left variable name in expression |
operator
PK
|
enum | Comparison operator: '<', '>', or '=' |
right_operand
PK
|
varchar | Right variable name in expression |
Primary Key: (left_operand, operator, right_operand)
Input & Output
Example 1 — Basic Boolean Evaluation
Input Tables:
Variables
| name | value |
|---|---|
| x | 66 |
| y | 77 |
Expressions
| left_operand | operator | right_operand |
|---|---|---|
| x | > | y |
| x | < | y |
| x | = | y |
| y | > | x |
Output:
| left_operand | operator | right_operand | value |
|---|---|---|---|
| x | > | y | false |
| x | < | y | true |
| x | = | y | false |
| y | > | x | true |
💡 Note:
We evaluate each expression by looking up variable values: x=66, y=77. Then: x>y becomes 66>77=false, x<y becomes 66<77=true, x=y becomes 66=77=false, y>x becomes 77>66=true.
Example 2 — Equal Values
Input Tables:
Variables
| name | value |
|---|---|
| a | 50 |
| b | 50 |
Expressions
| left_operand | operator | right_operand |
|---|---|---|
| a | = | b |
| a | > | b |
Output:
| left_operand | operator | right_operand | value |
|---|---|---|---|
| a | = | b | true |
| a | > | b | false |
💡 Note:
Both variables have equal values: a=50, b=50. So a=b evaluates to true, while a>b evaluates to false since 50 is not greater than 50.
Constraints
-
1 ≤ Variables.name.length ≤ 20 -
-1000 ≤ Variables.value ≤ 1000 -
operatoris one of'<','>','=' - All operands in expressions exist in Variables table
Visualization
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Understanding the Visualization
1
Input Tables
Variables with values and Expressions to evaluate
2
JOIN Operation
Join Variables twice to get operand values
3
Output
Evaluated boolean results
Key Takeaway
🎯 Key Insight: Use double JOINs when you need to compare values from the same lookup table
💡
Explanation
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