Does foreign key have to be primary key?

Can a table have only a foreign key and no primary key

You can create one without a primary key, or you can use a compound primary key, which involves creating a unique pair from the two references and using that pair as the unique identifying key. However, even this isnt necessary. (Note: Just because something isnt necessary doesnt mean it isnt “good practice”; it wouldnt typically be a good idea.

Can a foreign key be a primary key in the same table

As some responded, the answer is a resounding yes if you mean “can a foreign key “refer” to a primary key in the same table?” 8 September 2013

How is foreign key related to primary key

The primary key is defined as a column (or set of columns) where each value is unique and identifies a single row of the table, and the foreign key is defined as a column or a set of columns in one table that references the primary key columns in another table.11 Mar 2004

Can primary key and foreign key have different names

Yes, its alright.

Does foreign key need to be unique

Foreign key values are not required to be unique, but primary key values must.

Can a foreign key be null

Yes, a foreign key can be duplicated or NULL. Ill explain why one might need to be either. First, keep in mind that a foreign key only requires that the value in that field exists in the parent table, which is a different table, before it can be used as a foreign key.

How is foreign key different from primary key

A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables and uniquely identifies a record in the relational database table. A primary key is used to ensure that data in the specific column is unique.

Can you have a table with only a foreign key

Relational theory dictates that each table should have a candidate key; therefore, ideally, the business rule you mention would be in place to make the foreign key only table a “good” table. In your specific example, it would be OK to remove the OrderID.

Can a table have no primary key

The column or columns designated as the primary key ensure that the table is unique; no two rows can have the same key. Every table can have a primary key, but it is not required to have one.

Does foreign key need to be a primary key

Yes, a foreign key must be the primary key for the parent table. Yes, it may not be unique and may have duplicate entries in the child table, but it must be unique and free of duplicate entries at the parent table (since it is a primary key).

Can a table have both primary key and foreign key

A table can only have one primary key, which must be distinct and non-null, and any number of foreign keys. A foreign key may also contain duplicate values.

Can you create SQL table without primary key

No, a database table should not be created without a primary key. Each table must contain a column—or set of columns—that uniquely identifies one row.

Can a table have only primary key

This article explains how and why to use primary keys and how to set a tables primary key. Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key.

Can a table have 2 foreign keys

Depending on the need, a table may have multiple foreign keys. 26 Sept 2021

Is a foreign key a primary key

A foreign key is a field (or group of fields) in one table that refers to the primary key in another table. The table with the foreign key is referred to as the child table, and the table with the primary key is referred to as the referenced or parent table.

Can a table have a foreign key without a primary key

If the foreign key refers to a non-primary unique key, you must explicitly specify the column names of the key. A foreign key can refer to either a unique or a primary key of the parent table.

What is the difference between primary key and foreign key explain with example

A primary key is used to assure the value in the particular column is unique. The foreign key provides the link between the two tables.
Difference Between Primary Key and Foreign Key.

What is the use of primary key and foreign key in SQL with example

Difference Between Primary key vs Foreign key