Optimizing MySQL Indexing Performance

To effectively check the performance of MySQL indexing, you can utilize the following query:

EXPLAIN EXTENDED SELECT col1, col2, col3, COUNT(1) 
FROM table_name 
WHERE col1 = val 
GROUP BY col1 
ORDER BY col2;

SHOW WARNINGS;

By examining the output of this query, you can determine whether your query utilizes an index. To enhance performance further, consider creating a covering index. This involves adding columns in the following order:

1. Columns used in the WHERE clause
2. Columns used in the GROUP BY clause
3. Columns used in the ORDER BY clause
4. Columns used in the SELECT statement

For instance, for the provided query, you could implement a covering index as follows:

KEY(col1, col2, col3)

It's important to note that while adding additional indexes can optimize query performance, it may also slow down insert queries. Therefore, carefully consider the trade-offs and only create indexes that are essential for improving performance.