What methods can be used to improve performance when executing complex SQL queries?

To improve the performance of complex SQL queries, the following methods can be used:

• Indexing: creating indexes on columns involved in WHERE, JOIN, and ORDER BY clauses.
• Query optimization: rewriting queries to reduce the number of operations, using subqueries or joins efficiently.
• Using EXPLAIN: analyzing the execution plan of a query to identify bottlenecks.
• Caching results: if data does not change often, cache query results.
• Partitioning tables: reduces the amount of data to process.
• Parallel execution: utilizing database capabilities for parallel processing.

In Python, ORM with support for lazy loading and optimized queries can be used, for example, SQLAlchemy:

from sqlalchemy import create_engine, select
from sqlalchemy.orm import Session

engine = create_engine('postgresql://user:pass@localhost/db')

with Session(engine) as session:
    stmt = select(MyTable).where(MyTable.status == 'active')
    results = session.execute(stmt).scalars().all()

You can also profile queries and optimize them at the database level.