suresh **Difference between Clustered Index and Non-Clustered Index in SQL Server**
In SQL Server, a clustered index determines the physical order of the rows in a table, while a non-clustered index does not. Here are the key differences between the two types of indexes:
1. **Clustered Index**:
- In a clustered index, the rows of the table are stored in the order of the index key.
- It is the actual order of the data rows in the table.
- There can be only one clustered index per table.
- The leaf nodes of a clustered index contain the data pages of the table itself.
- Clustered indexes are efficient for range queries as they physically order the data.
2. **Non-Clustered Index**:
- In a non-clustered index, the index key values are stored separately from the actual data rows.
- It does not dictate the physical order of the data rows in the table.
- Multiple non-clustered indexes can be created on a single table.
- The leaf nodes of a non-clustered index contain pointers to the actual data rows.
- Non-clustered indexes are efficient for exact match queries.
**When to Use Clustered Index vs. Non-Clustered Index**:
- **Clustered Index**:
- Choose a clustered index when you frequently query ranges of data or when you need to retrieve data in the same order as the index key.
- Consider using a clustered index on columns that are often used in JOIN clauses.
- **Non-Clustered Index**:
- Use a non-clustered index when you frequently query individual rows or perform searches on columns that are not suitable for clustering.
- Non-clustered indexes are beneficial for queries that involve JOIN, WHERE, and ORDER BY clauses on columns that are not part of the clustered index.
In conclusion, understanding the differences between clustered and non-clustered indexes in SQL Server is essential for optimizing query performance and database design. Select the appropriate type of index based on the specific requirements of your application to improve overall database performance.
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