What is a non-clustered index in a database?
a) An index where the logical order of the index does not match the physical order of the rows
b) An index used for primary key columns
c) An index used to speed up updates and deletes
d) An index that enforces referential integrity
Answer:
a) An index where the logical order of the index does not match the physical order of the rows
Explanation:
A non-clustered index is an index where the logical order of the index does not match the physical order of the rows in the table. Unlike a clustered index, which dictates how the data is physically stored, a non-clustered index is a separate structure that references the data rows.
Non-clustered indexes are used to improve the performance of SELECT queries by providing a fast way to look up data without scanning the entire table. Multiple non-clustered indexes can exist on a single table, each providing a different path to retrieve data efficiently.
Non-clustered indexes are commonly used to optimize queries that search for data based on non-primary key columns.