Confirm Effective Index Usage in Query Execution

PostgreSQL: Verifying Index Usage with EXPLAIN

Write a PostgreSQL query to use EXPLAIN to verify that an index is utilized in a query filtering on an indexed column.

Solution:

-- Specify the action to check the query execution plan.
EXPLAIN  
-- Define the query to retrieve all columns from the Users table.
SELECT * FROM Users  
-- Add a condition to filter rows where the email matches the specified value.
WHERE email = '[email protected]'; 

Explanation:

• Purpose of the Query:
• To confirm that the query planner is using the appropriate index for efficient lookups.
• Ensures that the database leverages indexing to speed up searches.
• Key Components:
• WHERE email = '[email protected]' : The condition that should trigger index usage.
• EXPLAIN : Outputs the execution plan to inspect index scans.
• Real-World Application:
• Vital for troubleshooting slow queries and verifying that indexes are effective.

Notes:

• Review the plan output for terms like “Index Scan” to validate index usage.

For more Practice: Solve these Related Problems:

• Write a PostgreSQL query using EXPLAIN to verify that an index is used for filtering on the "username" column in the "Users" table.
• Write a PostgreSQL query using EXPLAIN to ensure an index is utilized in a JOIN between "Orders" and "Customers" on the foreign key column.
• Write a PostgreSQL query using EXPLAIN to check if an index scan is used for a query filtering on the "email" column in the "Contacts" table.
• Write a PostgreSQL query using EXPLAIN to confirm that a composite index is used for a query filtering on multiple columns in the "Transactions" table.

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