EXPLAIN ANALYZE for query profiling in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does EXPLAIN ANALYZE do in PostgreSQL?

EXPLAIN ANALYZE runs a SQL query and shows how PostgreSQL executes it, including the time taken for each step and the number of rows processed.

beginner

Why is EXPLAIN ANALYZE useful for query optimization?

It helps you see where the query spends time and which parts are slow, so you can improve indexes or rewrite the query for better speed.

intermediate

What is the difference between EXPLAIN and EXPLAIN ANALYZE?

EXPLAIN shows the planned steps without running the query. EXPLAIN ANALYZE runs the query and shows actual execution times and row counts.

intermediate

What kind of information does EXPLAIN ANALYZE output include?

It includes estimated and actual row counts, time spent on each step, and the order of operations in the query plan.

intermediate

How can you use EXPLAIN ANALYZE output to improve a slow query?

Look for steps with high time or many rows processed, then add indexes, rewrite joins, or reduce data scanned to speed up those parts.

What does EXPLAIN ANALYZE do in PostgreSQL?

A Creates a new index automatically

B Only shows the query syntax errors

C Deletes data from the database

D Runs the query and shows detailed execution steps with timing

EXPLAIN ANALYZE runs the query and shows how PostgreSQL executes it, including timing and row counts.

Which of these is NOT shown by EXPLAIN ANALYZE?

A The query result data

B Estimated rows to be processed

C Number of rows actually processed

D Actual time spent on each step

EXPLAIN ANALYZE does not show the query result data, only the execution plan and timing.

What is the main difference between EXPLAIN and EXPLAIN ANALYZE?

A <code>EXPLAIN ANALYZE</code> runs the query and shows actual times, <code>EXPLAIN</code> only shows the plan

B <code>EXPLAIN</code> runs the query, <code>EXPLAIN ANALYZE</code> does not

C They are exactly the same

D <code>EXPLAIN</code> deletes data, <code>EXPLAIN ANALYZE</code> updates data

EXPLAIN ANALYZE runs the query and shows actual execution times; EXPLAIN only shows the planned steps.

If a step in EXPLAIN ANALYZE shows a very high actual time, what should you consider?

A Ignoring it because it is normal

B Adding indexes or rewriting the query to optimize that step

C Deleting the table

D Restarting the database server

High time means that step is slow; optimizing it can improve query speed.

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

A SELECT * FROM table;

B EXPLAIN SELECT * FROM table;

C EXPLAIN ANALYZE SELECT * FROM table;

D ANALYZE TABLE table;

EXPLAIN ANALYZE runs the query and shows actual execution times.

Explain how EXPLAIN ANALYZE helps you understand and improve a slow query.

Think about what details you get from running the query with EXPLAIN ANALYZE.

Describe the difference between EXPLAIN and EXPLAIN ANALYZE in PostgreSQL.

One shows plan only, the other runs the query too.