What approaches and methods can be applied to improve the efficiency of executing complex SQL statements?

To improve the efficiency of complex SQL queries, the following approaches can be used:

• Indexing: create indexes on columns frequently used in filtering conditions and joins.
• Query optimization: avoid SELECT *, use only necessary fields.
• Query partitioning: break down complex queries into several simple ones, if possible.
• Using EXPLAIN: analyze the execution plan of the query to identify bottlenecks.
• Caching results: if data does not change often, save query results.
• Join optimization: use the correct types of JOINs and join conditions.

Example of using EXPLAIN in PostgreSQL:

EXPLAIN ANALYZE
SELECT * FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE o.amount > 1000;

This helps understand which operations take the most time and need optimization.