[Solved] You have a partial index:CREATE INDEX idx_recent_active ON users (last_login) WHERE active = true AND last_login > current_date - interval '30 days';Which query will NOT use this index? | PostgreSQL

PostgreSQL - Indexing Strategies

You have a partial index:

CREATE INDEX idx_recent_active ON users (last_login) WHERE active = true AND last_login > current_date - interval '30 days';

Which query will NOT use this index?

ASELECT * FROM users WHERE active = false AND last_login > current_date - interval '10 days';

BSELECT * FROM users WHERE active = true AND last_login > current_date - interval '15 days';

CSELECT * FROM users WHERE active = true AND last_login > current_date - interval '40 days';

DSELECT * FROM users WHERE active = true AND last_login > current_date - interval '30 days';

Step-by-Step Solution

Solution:

Step 1: Understand index condition
The index covers rows where active = true and last_login is within last 30 days.
Step 2: Analyze each query
The query filtering active = false is outside the index condition, so it won't use the index.
Final Answer:
SELECT * FROM users WHERE active = false AND last_login > current_date - interval '10 days'; -> Option A
Quick Check:
Query outside partial index WHERE = B [OK]

Quick Trick: Partial index used only if all WHERE conditions match index filter [OK]

Common Mistakes:

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You have a partial index: