SSC IMD SA 2017 – Question 184

Which statement is true about a clustered index?

• Clustered index is not associated with the table
• A clustered index is created by default on a unique key column
• A clustered index is not created on a unique key column
• None of these

Detailed Explanation:

The correct answer is b) A clustered index is created by default on the unique key/primary key column (क्लस्टर किए गए इंडेक्स अद्वितीय की कॉलम पर डिफ़ॉल्ट रूप से बनाया गया है).

In Relational Database Management Systems (such as Microsoft SQL Server and MySQL InnoDB):

• Physical Ordering: A Clustered Index sorts and physically stores the actual data rows of the table in the order of the indexed column(s). Because the physical data rows can only be sorted in one way on disk, there can only be one clustered index per table.
• Default Creation: When a table is defined with a PRIMARY KEY constraint, the RDBMS automatically creates a unique clustered index on that primary key column by default (unless a clustered index has already been designated or NONCLUSTERED is explicitly specified).
• Leaf Nodes: The leaf nodes of a clustered index contain the actual data pages of the table, eliminating the need for secondary lookups.