Do you know what a query plan is in a relational database?

A Query Plan or Execution Plan is a sequence of operations that a relational database management system (RDBMS) performs to retrieve the data requested by the user. It shows:

• Order of execution: Which tables will be processed first, the sequence of joins, filtering, and sorting.
• Access methods: How the RDBMS will access data from tables (full scan, index usage, etc.).
• Join methods: How data from different tables will be combined (e.g., nested loops, hashing, merge).
• Cost estimation: An estimate of resources (CPU time, disk access) needed to perform each operation.

The database query optimizer analyzes various possible plans and selects the one it estimates to be the most efficient. Viewing the query plan helps developers or database administrators understand why a particular query runs slowly and identify ways to optimize it (e.g., adding indexes, changing table structures, rewriting the query). Tools for viewing query plans can be specific to each RDBMS (e.g., EXPLAIN for PostgreSQL and MySQL, EXPLAIN PLAN FOR for Oracle).