What are the differences between a clustered and a non-clustered index?

Question

What are the differences between a clustered and a non-clustered index?

Answer 1

Clustered Index

• Only one clustered index can be there in a table
• Sort the records and store them physically according to the order
• Data retrieval is faster than non-clustered indexes
• Do not need extra space to store logical structure

Non Clustered Index

• There can be any number of non-clustered indexes in a table
• Do not affect the physical order. Create a logical order for data rows and use pointers to physical data files
• Data insertion/update is faster than clustered index
• Use extra space to store logical structure

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Apart from these differences you have to know that when table is non-clustered (when the table doesn't have a clustered index) data files are unordered and it uses Heap data structure as the data structure.