EXPLAIN ANALYZE for actual execution in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of EXPLAIN ANALYZE on a simple SELECT

Given the table employees(id INT, name TEXT, salary INT) with 3 rows, what does EXPLAIN ANALYZE SELECT * FROM employees WHERE salary > 50000; output?

PostgreSQL

EXPLAIN ANALYZE SELECT * FROM employees WHERE salary > 50000;

A The result rows of the SELECT query without any plan or timing information.

B Only the query plan without any timing or row count details.

C An error because EXPLAIN ANALYZE cannot be used with SELECT statements.

D A query plan showing a sequential scan with actual time and rows filtered, plus total execution time.

💡 Hint

EXPLAIN ANALYZE runs the query and shows actual execution details.

EXPLAIN ANALYZE executes the query and returns the query plan with actual timing and row counts, helping understand performance.

🧠 Conceptual

intermediate

Purpose of EXPLAIN ANALYZE in PostgreSQL

What is the main purpose of using EXPLAIN ANALYZE in PostgreSQL?

A To modify the query execution plan automatically for optimization.

B To show the estimated query plan without running the query.

C To execute the query and show the actual runtime statistics and plan.

D To display only the query syntax errors before execution.

💡 Hint

Think about what extra information EXPLAIN ANALYZE provides compared to EXPLAIN.

EXPLAIN ANALYZE runs the query and shows actual execution times and row counts, unlike EXPLAIN which only shows estimated plans.

📝 Syntax

advanced

Identify the correct EXPLAIN ANALYZE syntax

Which of the following is the correct syntax to get actual execution details for a query in PostgreSQL?

A EXPLAIN ANALYZE SELECT * FROM users WHERE age > 30;

B ANALYZE EXPLAIN SELECT * FROM users WHERE age > 30;

C EXPLAIN SELECT * FROM users WHERE age > 30 ANALYZE;

D SELECT EXPLAIN ANALYZE * FROM users WHERE age > 30;

💡 Hint

EXPLAIN ANALYZE is a prefix before the query.

The correct syntax is to write EXPLAIN ANALYZE before the query to run it and show execution details.

❓ optimization

advanced

Using EXPLAIN ANALYZE to find slow query parts

You run EXPLAIN ANALYZE on a complex query and see a nested loop join taking most of the time. What should you do next?

A Rewrite the query to remove all joins.

B Add indexes on join columns to speed up the nested loop.

C Ignore the nested loop because it is always the fastest join method.

D Disable EXPLAIN ANALYZE and run EXPLAIN only.

💡 Hint

Think about how indexes affect join performance.

Nested loops can be slow without indexes; adding indexes on join keys often improves performance.

🔧 Debug

expert

Diagnosing unexpected EXPLAIN ANALYZE output

You run EXPLAIN ANALYZE on a query but notice the actual execution time is much higher than expected. Which of these is NOT a likely cause?

A The EXPLAIN ANALYZE output is cached and shows old timings.

B The query is blocked by locks causing delays.

C The statistics used by the planner are outdated.

D The query plan uses sequential scans on large tables.

💡 Hint

Consider how EXPLAIN ANALYZE works and what affects timing.

EXPLAIN ANALYZE runs the query fresh each time; it does not cache timings. Other options can cause slow execution.