Does the execution plan from EXPLAIN always match what is actually executed?

The execution plan shown by the EXPLAIN command does not always fully match the actual query execution. This is because:

• The plan is an estimate by the optimizer at the time of query compilation, based on statistics and assumptions.
• Conditions may change during execution: caching, parallelism, locks, data modifications.
• Some DBMSs may apply dynamic optimization or adaptive execution.

Therefore, EXPLAIN is useful for understanding the execution logic and identifying bottlenecks, but for precise analysis, profiling and monitoring of actual execution should be used.