What are clustered and non-clustered indexes?

#Understanding Indexes in Databases

Indexes are crucial for optimizing the performance of database queries. They can be categorized into two main types: clustered indexes and non-clustered indexes. This document aims to clarify the differences between these two types of indexes.

#What is a Clustered Index?

A clustered index determines the physical order of data in a table. It is unique in that a table can have only one clustered index. The clustered index is created on the primary key by default, but it can be created on any column.

#Characteristics of Clustered Indexes

• Physical Order: The data rows are stored in the same order as the index.
• Single Index: A table can have only one clustered index.
• Performance: Clustered indexes can improve the performance of range queries.

#What is a Non-Clustered Index?

A non-clustered index, on the other hand, does not alter the physical order of the data. Instead, it creates a separate structure that points to the actual data rows. A table can have multiple non-clustered indexes.

#Characteristics of Non-Clustered Indexes

• Logical Order: The data is stored in a different order than the index.
• Multiple Indexes: A table can have multiple non-clustered indexes.
• Flexibility: Non-clustered indexes can be created on any column, providing more flexibility for query optimization.

#Key Differences Between Clustered and Non-Clustered Indexes

#Conclusion

In summary, understanding the differences between clustered and non-clustered indexes is essential for database optimization. Choosing the right type of index can significantly impact the performance of your database queries.