Can a table have two foreign key columns?
(One of them referenced two others, one at a time.) 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.
Where do I find the foreign key in SQL?
The column city_id is the foreign key in this table and indicates the value of the ID stored in the column id in the table city. We write FOREIGN KEY REFERENCES at the end of the definition of this column and follow it with the referenced table and column: city (id).
How to add new column with foreign key constraint in SQL?
As so often with SQL-related question, it depends on the DBMS. Some DBMS allow you to combine ALTER table operations separated by commas. For example… The syntax for IBM DB2 LUW is similar, repeating the keyword ADD but (if I read the diagram correctly) not requiring a comma to separate the added items.
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.
How are foreign keys made primary keys in SQL Server?
(The respective columns in the other two tables are made primary keys accordingly.) The CK_Ticket_GroupUser check constraint ensures that only one of the two foreign key columns contains a reference (the other being NULL, that’s why both have to be nullable).
How to create multiple table in SQL Server?
CREATE TABLE dbo.Group ( ID int NOT NULL, Name varchar (50) NOT NULL ) CREATE TABLE dbo.User ( ID int NOT NULL, Name varchar (50) NOT NULL ) CREATE TABLE dbo.Ticket ( ID int NOT NULL, Owner int NOT NULL, Subject varchar (50) NULL ) Users belong to multiple groups. This is done via a many to many relationship, but irrelevant in this case.