Databricks SQL Tutorial: Using Query Hints Deliberately

This tutorial will guide you through using query hints in Databricks SQL. Query hints are directives you can add to your SQL queries to influence the optimizer’s choices, potentially improving performance or ensuring specific execution strategies. This tutorial focuses on demonstrating and understanding how to use these hints effectively.

Script 1: Basic BRUTE Hint for Optimization

This script demonstrates a simple `BRUTE` hint to force the optimizer to use a full table scan instead of a more optimized plan. We’ll create a small table and then use the hint to force a full scan.

The `BRUTE` hint tells the optimizer to use a full table scan. It can be helpful when you know the data distribution is very uniform and the optimizer is making suboptimal decisions based on statistics. This is a simple use case and in most scenarios, the SQL optimizer will choose the best plan automatically.

The final SELECT statement returns the entire `sales` table.

Script 2: FORCE ORDER Hint

This script introduces the `FORCE ORDER` hint to control the order in which the database engine processes rows. This is especially useful when the data is physically organized in a way that’s different from the query’s logical order.

The `FORCE ORDER` hint instructs the database engine to process the rows in the order they are physically stored. This can be useful when the data has been sorted differently than the query expects. In this minimal case, it may not significantly affect performance, but it showcases the hint’s purpose.

The final SELECT statement returns the entire `orders` table.

Script 3: BRUTE Hint with FORCE ORDER

This script combines the `BRUTE` and `FORCE ORDER` hints. This demonstrates how combining hints can be used to force a particular execution strategy. In more complex scenarios, this may improve performance by ensuring the database doesn’t make incorrect decisions based on statistics.

This script utilizes both hints. `BRUTE` forces a full table scan, and `FORCE ORDER` ensures the rows are processed in their physical order. These combinations will typically optimize performance when data is physically organized in a way that deviates from the query.

The final SELECT statement returns the entire `products` table.