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Posted on    December-13-2010 12:00 AM

 MSSQL Server MSSQL Server 
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Amit Singh

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Posted on    December-13-2010 1:00 AM

Primary Key

  • The column or columns of the table whose value uniquely identifies each row in the table is called primary key.
  • You can define column as primary key using primary key constraint while you create table.
  • When you define a column as primary key, a unique index is created which restricts duplicate data and fast access to data.
  • A column defined as primary key doesn’t allow null value.
  • By default, clustered index in created with the column having primary key.

Unique key

  • Unique key also ensures data uniqueness like primary key.
  • A column with unique key defined allows null value.
  • By default, it creates non-clustered index.

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