How to choose an index to optimize query speed?

To choose an index that optimizes query speed, you need to analyze which fields are most frequently used in WHERE, JOIN, ORDER BY, and GROUP BY clauses. It's better to create indexes on columns that are often used for filtering or sorting data.

Main recommendations:

• Use composite indexes if queries filter on multiple columns.
• Avoid redundant indexes as they slow down insert and update operations.
• Analyze query execution plans (EXPLAIN in SQL) to understand which indexes are used.
• For large text fields or JSON data, it is better to use specialized index types (e.g., full-text indexes).

Example: if a query like SELECT * FROM users WHERE last_name = 'Ivanov' AND age > 30 is frequently executed, consider creating an index on (last_name, age).