FAQ: Intermediate Indexes - Index-Only Scans

Frequently Asked Questions SQL FAQ
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This community-built FAQ covers the “Index-Only Scans” exercise from the lesson “Intermediate Indexes”.

Paths and Courses
This exercise can be found in the following Codecademy content:

Design Databases With PostgreSQL

FAQs on the exercise Index-Only Scans

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2

I don’t see what information displays the change in lookup behavior for the query.

Query Results
QUERY PLAN
Bitmap Heap Scan on customers (cost=12.29..1003.86 rows=500 width=304) (actual time=0.251..1.729 rows=993 loops=1)
  Recheck Cond: ((last_name)::text = 'Smith'::text)
  Heap Blocks: exact=713
  -> Bitmap Index Scan on customers_idx (cost=0.00..12.17 rows=500 width=0) (actual time=0.170..0.170 rows=993 loops=1)
        Index Cond: ((last_name)::text = 'Smith'::text)
Planning time: 0.248 ms
Execution time: 1.805 ms
QUERY PLAN
Bitmap Heap Scan on customers (cost=12.29..1003.86 rows=500 width=304) (actual time=0.173..0.844 rows=993 loops=1)
  Recheck Cond: ((last_name)::text = 'Smith'::text)
  Heap Blocks: exact=713
  -> Bitmap Index Scan on customers_idx (cost=0.00..12.17 rows=500 width=0) (actual time=0.098..0.098 rows=993 loops=1)
        Index Cond: ((last_name)::text = 'Smith'::text)
Planning time: 0.113 ms
Execution time: 0.897 ms

EXPLAIN ANALYZE SELECT
  first_name,
  last_name,
  email_address
FROM customers
WHERE last_name = 'Smith';

CREATE INDEX customers_last_name_first_name_email_address_idx ON customers(last_name, first_name, email_address);

EXPLAIN ANALYZE SELECT
  first_name,
  last_name,
  email_address
FROM customers
WHERE last_name = 'Smith';
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