Do you know what a query plan is and how to view it?

The query plan is a detailed description of how the DBMS will execute an SQL query. It shows the order of operations, used indexes, join methods, and estimated execution costs.

The plan helps understand why a query runs slowly and identifies opportunities for optimization.

How to view a query plan:

• In PostgreSQL, you can use the EXPLAIN command before the query, for example:

EXPLAIN SELECT * FROM orders WHERE customer_id = 123;

• For a more detailed plan with timing estimates and statistics, use EXPLAIN ANALYZE:

EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;

• In other DBMSs, such as MySQL, there are similar EXPLAIN commands.

By analyzing the plan, you can see which indexes are used, whether full table scans are performed, and based on this, improve the query or data structure.