LeetCode 1757: Recyclable and Low Fat Products — SQL Solution

 

Problem Statement:

The task is to write an SQL query to find the IDs of products that are both recyclable and low fat. You are given a table called Products with the following structure:

• product_id: Integer, unique identifier for each product.
• low_fats: Character ('Y' or 'N'), indicates whether the product is low fat.
• recyclable: Character ('Y' or 'N'), indicates whether the product is recyclable.

Table: Products

Column Name	Data Type
product_id	int
low_fats	enum('Y', 'N')
recyclable	enum('Y', 'N')

Task:

Write a query to return the product_id of products that are both low fat and recyclable.

Example:

Input:

product_id	low_fats	recyclable
1	'Y'	'N'
2	'Y'	'Y'
3	'N'	'Y'
4	'Y'	'Y'

Output:

product_id
2
4

Explanation:

• Product with product_id = 2 is low fat and recyclable.
• Product with product_id = 4 is also low fat and recyclable.
• Other products either don't meet one or both conditions.

Solution Approach

The problem is simple, requiring us to filter the products based on two conditions:

1. The product must be low fat (low_fats = 'Y').
2. The product must be recyclable (recyclable = 'Y').

This means we need to use an SQL SELECT statement with a WHERE clause that checks both conditions.

SQL Query Solution:

select product_id from Products where low_fats ='Y' AND recyclable ='Y';

Breakdown of the Solution:

• SELECT product_id: We want to retrieve the product_id of products that meet our criteria.
• FROM Products: Specifies the table from which we're retrieving data.
• WHERE low_fats = 'Y' AND recyclable = 'Y': This is the condition that filters products. We only select products where both the low_fats and recyclable columns are marked as 'Y'.

Optimizations and Considerations:

• Indexes: Ensure the low_fats and recyclable columns are indexed if this query is part of a larger application, as this will speed up the filtering process, especially for large datasets.
• Enum vs String Comparison: In many databases, the enum data type is optimized for performance compared to regular strings. However, in some SQL dialects (e.g., MySQL), 'Y' and 'N' values can be treated like simple strings.

Time Complexity:

• The time complexity of this query is O(n), where n is the number of rows in the Products table. Since we're applying a filter on two columns, it requires scanning the table (unless indexes are in place).

Space Complexity:

• The space complexity is O(1), as the query does not require any extra space that scales with the size of the input.

Edge Cases:

1. No products meet the criteria: The query will return an empty result set if no products are both low fat and recyclable.
2. All products meet the criteria: If all products are both low fat and recyclable, the query will return all the product IDs.
3. Mixed case entries: Depending on how your SQL database handles case sensitivity, be mindful of mixed-case entries for 'Y' and 'N' values. Ensure the data is consistent, or use functions like UPPER() or LOWER() to standardize comparisons (though it may affect performance).

Conclusion:

LeetCode Problem 1757, "Recyclable and Low Fat Products," is a simple yet practical example of filtering data using SQL's WHERE clause. By understanding how to structure queries and apply conditions efficiently, you can handle similar product filtering scenarios in real-world applications.