SQL query optimization: what did it consist of?

SQL query optimization typically involves several key aspects:

• Indexing: creating and using indexes to speed up data retrieval.
• Avoiding redundant operations: for example, minimizing the number of JOINs, using WHERE to filter data as early as possible.
• Using EXPLAIN: analyzing the query execution plan to identify bottlenecks.
• Optimizing subqueries: replacing subqueries with JOINs if it improves performance.
• Selecting necessary columns: instead of SELECT *, choose only the required fields.

Example:

-- Non-optimized query
SELECT * FROM orders o JOIN customers c ON o.customer_id = c.id WHERE c.status = 'active';

-- Optimized query
SELECT o.id, o.date, c.name FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.status = 'active';

Here, we select only the necessary fields, which reduces network and memory load.