If a composite index is created on columns (A, B), which query will NOT fully benefit from this index?

easy📝 Conceptual Q2 of 15

SQL - Indexes and Query Performance

ASELECT * FROM table WHERE B = 20;

BSELECT * FROM table WHERE A = 10;

CSELECT * FROM table WHERE A = 10 ORDER BY B;

DSELECT * FROM table WHERE A = 10 AND B = 20;

Step-by-Step Solution

Solution:

Step 1: Review composite index usage
Composite index on (A, B) helps queries filtering on A or both A and B, but not on B alone.
Step 2: Analyze each query
Query filtering only on B cannot use the index efficiently because A is the first column.
Final Answer:
SELECT * FROM table WHERE B = 20; -> Option A
Quick Check:
Index on (A,B) can't optimize filter on B alone = D [OK]

Quick Trick: Index first column must be in WHERE for full benefit [OK]

Common Mistakes:

Master "Indexes and Query Performance" in SQL

9 interactive learning modes - each teaches the same concept differently

Want More Practice?

15+ quiz questions · All difficulty levels · Free

More SQL Quizzes