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Why we need non clustered index in SQL Server?
A non-clustered index helps you to creates a logical order for data rows and uses pointers for physical data files. Allows you to stores data pages in the leaf nodes of the index. By Default Primary Keys Of The Table is a Clustered Index. It can be used with unique constraint on the table which acts as a composite key.
Does a non clustered index have to be unique?
Both clustered and nonclustered indexes can be unique. This means no two rows can have the same value for the index key. Otherwise, the index is not unique and multiple rows can share the same key value.
Does unique key create non clustered index?
By default the unique constraint and Unique index will create a non clustered index if you don’t specify any different (and the PK will by default be created as CLUSTERED if no conflicting clustered index exists) but you can explicitly specify CLUSTERED / NONCLUSTERED for any of them.
How are non clustered indexes created in SQL Server?
When you create a UNIQUE constraint, a unique Non-clustered index will be created automatically to enforce that constraint. Non-clustered indexes can be created independently of the constraints using the SQL Server Management Studio New Index dialog box or using the CREATE INDEX T-SQL command.
Can a unique key be a clustered index?
A table can contain only one clustered index and a primary key can be a clustered / non-clustered index. Unique Key can be a clustered/non-clustered index as well, below are some of the examples Scenario 1 : Primary Key will default to Clustered Index
How to make an index Unique in SQL?
For indexes that are not specified as unique SQL Server will silently make them unique any way. For clustered indexes this is done by appending a uniquefier to duplicate keys.
Is there maximum capacity for clustered indexes in SQL Server?
For details about index key limits see Maximum Capacity Specifications for SQL Server. Both clustered and nonclustered indexes can be unique. This means no two rows can have the same value for the index key. Otherwise, the index is not unique and multiple rows can share the same key value.