SQL Server Notification Services Question:
Define Primary and Unique key?
Answer:
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.
► 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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