Optimizing Subqueries in MySQL with EXPLAIN

Analyze Subquery Performance with EXPLAIN

Write a MySQL query that uses EXPLAIN to analyze the performance of a query with a subquery that retrieves orders for customers from Berlin.

Solution:

-- Use EXPLAIN to analyze a query with a subquery filtering orders for customers from Berlin.
EXPLAIN SELECT * FROM Orders
WHERE CustomerID IN (
    SELECT CustomerID FROM Customers WHERE City = 'Berlin'
);

Explanation:

• Purpose of the Query:
• To analyze the execution plan of a query that includes a subquery.
• Helps in identifying potential inefficiencies in subquery execution.
• Key Components:
• EXPLAIN : Initiates the performance analysis.
• IN (SELECT CustomerID FROM Customers WHERE City = 'Berlin') : The subquery filters customers based on their city.
• Real-World Application:
• Useful for optimizing queries that retrieve data based on relationships between tables with subqueries.

Notes:

• Consider rewriting subqueries as JOINs if performance issues are detected.
• Use EXPLAIN to compare the performance of different query structures.

For more Practice: Solve these Related Problems:

• Write a MySQL query to use EXPLAIN to analyze the performance of a query with a subquery that retrieves employees from departments with more than 10 members.
• Write a MySQL query to use EXPLAIN to analyze the performance of a query with a subquery that retrieves products with prices higher than the average price.
• Write a MySQL query to use EXPLAIN to analyze the performance of a query with a subquery that retrieves orders placed by customers who have made more than 5 purchases.
• Write a MySQL query to use EXPLAIN to analyze the performance of a query with a subquery that retrieves users who belong to roles with administrative privileges.

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous MySQL Exercise: Force Index usage in a Query.
Next MySQL Exercise: Utilize Covering Index for Query Optimization.