EXPLAIN ANALYZE for actual execution in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does EXPLAIN ANALYZE do in PostgreSQL?

EXPLAIN ANALYZE runs a query and shows the actual steps PostgreSQL took to execute it, including time spent on each step and the number of rows processed.

beginner

Why is EXPLAIN ANALYZE useful compared to just EXPLAIN?

Unlike EXPLAIN which only shows the planned steps, EXPLAIN ANALYZE actually runs the query and shows real execution times and row counts, helping find slow parts.

intermediate

What kind of information does EXPLAIN ANALYZE output include?

• Execution time for each step
• Number of rows processed
• Actual vs estimated rows
• Cost estimates

intermediate

How can EXPLAIN ANALYZE help improve query performance?

By showing which steps take the most time or process more rows than expected, it helps identify bottlenecks and guides changes like adding indexes or rewriting queries.

beginner

Does EXPLAIN ANALYZE modify data when running a query?

No, it runs the query normally, so if the query changes data (like INSERT or UPDATE), those changes will happen.

Use it carefully with data-changing queries.

What does EXPLAIN ANALYZE show that EXPLAIN does not?

A Syntax errors in the query

B Only the query plan without execution

C Actual execution time and row counts

D Database schema details

EXPLAIN ANALYZE runs the query and shows real execution details, unlike EXPLAIN which only shows the planned steps.

Which of these is NOT included in EXPLAIN ANALYZE output?

A Estimated cost of query steps

B User permissions for the query

C Number of rows processed

D Actual time spent on each step

User permissions are not shown by EXPLAIN ANALYZE. It focuses on query execution details.

If a query modifies data, what happens when you run it with EXPLAIN ANALYZE?

A Only a simulation is done without execution

B The query runs but data is not changed

C The query is blocked from running

D The data changes are applied as usual

EXPLAIN ANALYZE runs the query normally, so data changes happen if the query modifies data.

How can EXPLAIN ANALYZE help you improve a slow query?

A By showing which steps take the most time

B By automatically fixing the query

C By deleting unnecessary data

D By increasing server memory

It helps identify slow parts of the query so you can optimize them.

Which command would you use to see the actual execution plan of a query in PostgreSQL?

A EXPLAIN ANALYZE SELECT * FROM table;

B SHOW PLAN SELECT * FROM table;

C DESCRIBE SELECT * FROM table;

D RUN PLAN SELECT * FROM table;

EXPLAIN ANALYZE runs the query and shows the actual execution plan.

Explain in your own words what EXPLAIN ANALYZE does and why it is useful.

Think about how seeing real times helps improve queries.

Describe the difference between EXPLAIN and EXPLAIN ANALYZE.

One just plans, the other runs and measures.