Can I have the same field as primary key and foreign key in mysql?

You can create a column having both keys (primary and foreign) but then it will be one to one mapping and add uniqueness to this column.

Can we have primary key and foreign key in same table?

A table can have multiple unique keys and foreign keys, but only one primary key. All foreign keys must reference a corresponding primary or unique key that matches the column types of each column in the foreign key. The primary key for a foreign key can be on a different table or the same table as the foreign key.

Can primary key have unique values?

A primary key column cannot contain NULL values, whereas a unique key can have NULL values, but only one NULL is allowed in a table. A primary key should be unique, but a unique key cannot necessarily be the primary key.

Does the foreign key have to be unique?

3 Answers. By the SQL standard, a foreign key must reference either the primary key or a unique key of the parent table. If the primary key has multiple columns, the foreign key must have the same number and order of columns.

Do foreign key names have to be unique?

Creating a foreign key is almost as easy as creating a primary key, except that SQL Server imposes several more rules on foreign keys. For example, the foreign key must reference a primary key or unique constraint, although that reference can be on the same table or on a different table.

Does foreign key have to be unique?

Is primary key and unique key same?

Key Differences Between Primary key and Unique key: Primary key will not accept NULL values whereas Unique key can accept NULL values. A table can have only one primary key whereas there can be multiple unique key on a table.

Is unique key and candidate key are same?

Candidate key is a set of columns which can uniquely identify the values in a table and can act as a unique key. One of these candidate keys will become the primary key and the rest will become alternate keys. Unique key as the name suggests , is used to uniquely identify a value in a table. For example Emp_id etc.

Can a primary key references another primary key?

Yes, it is legal to have a primary key being a foreign key. This is a rare construct, but it applies for: a 1:1 relation. The two tables cannot be merged in one because of different permissions and privileges only apply at table level (as of 2017, such a database would be odd).

What is difference between primary key and unique key?

Can a primary key reference another primary key?