SQL Index Optimization MCQ Composite and Covering Indexes Practice Questions

Direction: Choose the correct option

What is a composite index?

A. Index on multiple columns

B. Unique index

C. Primary key

D. Index on one column

Direction: Choose the correct option

CREATE INDEX idx_name ON employees(last_name, first_name);

Which query will use this index?

A. WHERE first_name = 'John'

B. WHERE last_name LIKE '%son'

C. WHERE first_name LIKE 'J%'

D. WHERE last_name = 'Smith'

Direction: Choose the correct option

What is a covering index?

A. Index that covers entire table

B. Index on all tables

C. Primary key index

D. Index containing all needed columns

Direction: Choose the correct option

SELECT dept_id, salary FROM employees WHERE dept_id = 5;

What index would cover this query?

A. INDEX(dept_id)

B. INDEX(dept_id, salary)

C. INDEX(salary)

D. PRIMARY KEY

Direction: Choose the correct option

When can indexes hurt performance?

A. Only help selects

B. Only on large tables

C. Too many indexes on write-heavy tables

D. Always help

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