The different types of KEYS in sql server are:

 A candidate key acts as a unique key. A unique key can be a PRIMARY key. A candidate key can be a single COLUMN or combination of columns. Multiple candidate keys are allowed in a table.

Primary Key:

• To uniquely identify a row, Primary key is used.
• A table allows only one Primary key
• A Primary key can be a single column or combination of columns.

 Foreign Key:

A foreign key in a table is a key which refer ANOTHER table’s primary key . A primary key can be referred by multiple foreign keys from other tables. It is not required for a primary key to be the REFERENCE of any foreign keys. The interesting part is that a foreign key can refer back to the same table but to a different column. This kind of foreign key is known as “self-referencing foreign key”.

The different types of Keys in sql server are:

 A candidate key acts as a unique key. A unique key can be a Primary key. A candidate key can be a single column or combination of columns. Multiple candidate keys are allowed in a table.

Primary Key:

 Foreign Key:

A foreign key in a table is a key which refer another table’s primary key . A primary key can be referred by multiple foreign keys from other tables. It is not required for a primary key to be the reference of any foreign keys. The interesting part is that a foreign key can refer back to the same table but to a different column. This kind of foreign key is known as “self-referencing foreign key”.