Bird
0
0

When does using an index typically improve query performance in a database?

easy📝 Conceptual Q1 of 15
SQL - Indexes and Query Performance
When does using an index typically improve query performance in a database?
AWhen the query filters on a column with many unique values
BWhen the query scans the entire table without filtering
CWhen the table has very few rows
DWhen the query updates all rows in the table
Step-by-Step Solution
Solution:

  1. Step 1: Understand index usage for filtering

    Indexes help when queries filter on columns with many unique values because they can quickly locate matching rows.

  2. Step 2: Compare with full table scans

    If the query scans the entire table or updates all rows, indexes do not help and may slow down performance.

  3. Final Answer:

    When the query filters on a column with many unique values -> Option A

  4. Quick Check:

    Index helps with selective filtering = A [OK]
Quick Trick: Indexes help most with selective filters on unique columns [OK]
Common Mistakes:
  • Thinking indexes help full table scans
  • Assuming indexes speed up updates on all rows
  • Believing indexes help small tables always

Want More Practice?

15+ quiz questions · All difficulty levels · Free

Free Signup - Practice All Questions
More SQL Quizzes
CASE Expressions - CASE in WHERE clause - Quiz 4medium Common Table Expressions (CTEs) - Multiple CTEs in one query - Quiz 3easy Common Table Expressions (CTEs) - Recursive CTE concept - Quiz 6medium Database Design and Normalization - Star schema concept - Quiz 11easy Indexes and Query Performance - How an index works (B-tree mental model) - Quiz 6medium Indexes and Query Performance - Single column index - Quiz 6medium SQL Security Basics - Why SQL security awareness matters - Quiz 9hard Stored Procedures and Functions - Parameters (IN, OUT, INOUT) - Quiz 9hard Transactions and Data Integrity - Why transactions are needed - Quiz 12easy Window Functions Fundamentals - OVER clause with ORDER BY - Quiz 4medium