Define Primary and Unique key?
Submitted by: AdministratorPrimary 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.
Submitted by: Administrator
► 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.
Submitted by: Administrator
Read Online SQL Notification Services Job Interview Questions And Answers
Top SQL Notification Services Questions
☺ | Explain OPENQUERY function and OPENROWSET function? |
☺ | Define data, entity, domain and referential integrity? |
☺ | Define transaction and transaction isolation levels? |
☺ | How does Notification Services Work? |
☺ | What is Isolation Levels? |
Top Databases Programming Categories
☺ | RDBMS Interview Questions. |
☺ | SQL Interview Questions. |
☺ | SSRS Interview Questions. |
☺ | Database Administrator (DBA) Interview Questions. |
☺ | Sybase Interview Questions. |