MySQL Range Partition Pruning Not Working Fix

In this tutorial, you'll learn about MySQL Range Partition Pruning Not Working Fix. We cover key concepts, practical examples, and best practices.

Range partitioned table queries are scanning all partitions because the WHERE clause uses an equality condition that MySQL cannot match to partition boundaries.

The Wrong Way

EXPLAIN SELECT * FROM orders WHERE order_date = '2025-06-01'\G

Output:

partitions: p2025Q1,p2025Q2,p2025Q3,p2025Q4 -- All partitions scanned

The Right Way

EXPLAIN SELECT * FROM orders WHERE order_date >= '2025-06-01' AND order_date < '2025-06-02'\G

Output:

partitions: p2025Q2 -- Only relevant partition scanned

Step-by-Step Fix

1. Use range conditions (>= AND <) instead of equality for better pruning

2. Ensure the partition key is not wrapped in any function

3. Check EXPLAIN PARTITIONS for 'partitions' column to see which are scanned

4. Use TO_DAYS() for DATE partition keys to enable pruning

5. Avoid VARCHAR partition keys -- use integer or date types for range partitioning

Prevention Tips

• Test all queries with the database's explain plan tool before deploying to production.
• Monitor query performance trends using built-in monitoring tools.
• Set up automated index usage analysis in CI/CD pipelines.
• Review database configuration quarterly against workload patterns.
• Keep database statistics up to date with regular maintenance operations.
• Use DodaTech's monitoring tools to track query performance regressions.

Common Mistakes with partition range

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world MYSQL code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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