How to solve the issue of “mysql prompt force index”?

If you encounter issues when using the FORCE INDEX keyword in MySQL to force the query optimizer to use a specific index, you can try the following methods to resolve them:

1. Ensure index existence: Before using FORCE INDEX, make sure the index you specify actually exists in the table. You can use the statement SHOW INDEX FROM tablename to check the table’s index status.
2. Optimize query: when using FORCE INDEX, the query optimizer will ignore any other potential indexes. So, make sure your query has been optimized and no other more suitable index is available before using FORCE INDEX.
3. Instead of using FORCE INDEX, you can opt for USE INDEX as a hint to the query optimizer for which index to use, without forcing it. It allows the optimizer to still choose a more suitable index if available, so using USE INDEX can be a good alternative if you are unsure about forcing a specific index.
4. Check index selectivity: The selectivity of an index refers to the uniqueness of different values in the index. If the selectivity of an index is low, meaning the values in the index are very similar, then forcing the use of that index may not necessarily improve query performance. Before using FORCE INDEX, you can use the statement SHOW INDEX FROM tablename to check the selectivity of the index.

In summary, the key to solving the FORCE INDEX issue is to ensure the existence of indexes, optimize queries, use appropriate indexes, and make reasonable selectivity choices.