Define Primary And Unique Key?

1.	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. Primary Key Unique key

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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

Primary Key

Unique key

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