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I created a new table and set ID as a primary key and in the folder index I found PK__NewEmp__3214EC27634FE916 clustered

I want to create another Index on Salary column is it possible? Also, I want to know What the advantages of an index in SQL Server and what's the difference between clustered index and non-clustered index?

clustered index VS non-clustered index in SQL Server

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What're Indexes in SQL Server?

Indexes are used to retrieve data from the database more quickly. The users cannot see the indexes, they are just used to speed up searches/queries.

Clustered Index Vs non-clustered Index

Clustered index: determine the physical order of data.
The table can have only one Cluster index, and Cluster Index can be one-column or two-column

Note: If you add a primary key for a table its automatically becomes a clustered index.

Non clustered indexes: have a structure separate from the data rows.
A non clustered index contains the non clustered index key values and each key-value entry has a pointer to the data row that contains the key value.

Note You can create many nonclustered indexes

To Create Nonclustered for the salary table, you can use this query:

Create Nonclustered Index IX_TableName_Salary
on TableName (Salary)

For more details, you can also see Clustered and Nonclustered Indexes

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