Optimize MySQL Queries & Performance

The following measures can be taken to optimize query statements and database performance in MySQL:

1. Creating indexes for frequently queried columns can improve query performance, but be cautious not to over-index as it can increase the cost of write operations.
2. Avoid using SELECT: Try to avoid using SELECT as much as possible and only query the columns that are needed. This can reduce the amount of data being queried and improve query efficiency.
3. Ensure that the columns used for joining in a JOIN query have appropriate indexes.
4. Use the EXPLAIN command to view the query execution plan and check for any inefficient indexes or query methods.
5. Avoid using subqueries: It is preferable to avoid using subqueries, as they can be rewritten as JOIN queries to improve performance.
6. Avoid using the OR and IN operators: these operators can cause full table scans, impacting performance.
7. Optimizing table structure, by normalizing and appropriately denormalizing tables, can improve query efficiency.
8. Avoid using a large amount of OR and NOT operators as they can lead to full table scans and impact performance.
9. Regularly cleaning out unnecessary data can reduce the burden on the database and improve performance.
10. Using cache: Utilizing cache can decrease the frequency of queries to the database and enhance performance.

Using the above methods can optimize query statements and database performance to improve MySQL database performance.