Does foreign key have to be primary in another table?

Does foreign key have to be primary in another table?

A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table. So in your case if you make AnotherID unique, it will be allowed.

How do foreign keys of tables relate to primary keys?

A primary key is a column or a set of columns in a table whose values uniquely identify a row in the table. A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table.

Which table should have the foreign key?

child table
The table that contains the foreign key is considered the child table, and the table that the foreign key references is the parent table. The foreign key restricts what data can be stored in the foreign key columns in the child table, based on the data in the referenced columns in the parent table.

Can we create primary key and foreign key on same table?

A foreign key constraint doesn’t have to be linked only to a primary key constraint in another table. FOREIGN KEY constraints can reference another column in the same table, and is referred to as a self-reference. A FOREIGN KEY constraint specified at the column level can list only one reference column.

How many primary and foreign keys can a table have?

A table can contain only one primary key constraint.

Why should we use primary foreign keys?

Essentially, primary and foreign keys are used as a way to constrain or link related data in a database. This ensures that data remains consistent and that the database contains no redundant data. For example, if you delete a table (or even a row in a table) that other tables rely on, the redundant data is removed.

How to create a table with foreign key?

So, the referencing table had two foreign key columns, and also it had a constraint to guarantee that exactly one table (not both, not neither) was referenced by a single row. CREATE TABLE dbo. [Group] ( ID int NOT NULL CONSTRAINT PK_Group PRIMARY KEY, Name varchar (50) NOT NULL ); CREATE TABLE dbo.

How to create nullable foreign keys in SQL Server?

You could simply create two columns in Ticket, OwnedByUserId and OwnedByGroupId, and have nullable Foreign Keys to each table. You could create M:M reference tables enabling both ticket:user and ticket:group relationships.

Is there limit to number of foreign keys in SQL Server?

A table can reference a maximum of 253 other tables and columns as foreign keys (outgoing references). SQL Server 2016 (13.x) increases the limit for the number of other table and columns that can reference columns in a single table (incoming references), from 253 to 10,000.

Is there a limit to the number of foreign key references?

Greater than 253 foreign key references are not currently available for columnstore indexes, memory-optimized tables, Stretch Database, or partitioned foreign key tables. Unlike primary key constraints, creating a foreign key constraint does not automatically create a corresponding index.