When Should You Use MySQL\'s STRAIGHT_JOIN Instead of INNER JOIN?

When to Use STRAIGHT_JOIN in MySQL

In MySQL, the STRAIGHT_JOIN keyword enforces a specific join order, overriding the optimizer's default plan. This can improve performance when the optimizer has chosen a suboptimal plan. However, it's important to understand when to use STRAIGHT_JOIN and when to stick with the default INNER JOIN.

Use STRAIGHT_JOIN When:

• Table Order is Critical: STRAIGHT_JOIN guarantees the join order specified in the query. This can be beneficial when the join order significantly impacts the performance or correctness of the query.
• Optimizer Choosing Poor Plan: If the optimizer consistently chooses a suboptimal query plan for a particular query, using STRAIGHT_JOIN can force it to use a specific plan.

Use INNER JOIN When:

• Optimizer Optimizing Well: In general, the MySQL optimizer is capable of choosing efficient query plans. Using STRAIGHT_JOIN unnecessarily can limit the optimizer's flexibility and potentially result in reduced performance.
• Data Distribution Changes: The distribution of data in tables can change over time. If STRAIGHT_JOIN is used to enforce a specific join order, it may become outdated as the data distribution changes, resulting in suboptimal performance.

Recommendation:

Avoid using STRAIGHT_JOIN as a default strategy. Instead, start with regular INNER JOINs. If you encounter a performance problem, investigate the query plan using EXPLAIN and consider using STRAIGHT_JOIN only if there is a clear benefit. Additionally, keep in mind that STRAIGHT_JOIN should be used sparingly as data distribution or index selectivity can change over time, rendering the join order specified by STRAIGHT_JOIN suboptimal.

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