Table of Contents
- 1 Can 1 foreign key reference multiple tables?
- 2 Can two tables share a foreign key?
- 3 Can two tables reference each other in SQL?
- 4 Can a table have multiple primary keys?
- 5 How do you create a relationship between two tables in SQL?
- 6 How can I have two foreign keys in SQL?
- 7 Why does the referencing table have two foreign key columns?
- 8 Can a foreign key be used as a primary key?
- 9 Can a single column in a table reference multiple tables?
Can 1 foreign key reference multiple tables?
The FOREIGN KEY constraint differs from the PRIMARY KEY constraint in that, you can create only one PRIMARY KEY per each table, with the ability to create multiple FOREIGN KEY constraints in each table by referencing multiple parent table.
A table may have multiple foreign keys, and each foreign key can have a different parent table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys.
Can a foreign key reference multiple columns?
MySQL allows us to add a FOREIGN KEY constraint on multiple columns in a table. The condition is that each Foreign Key in the child table must refer to the different parent table.
Can two tables reference each other in SQL?
When you create two tables that are related to each other, they are often related by a column in one table referencing the primary key of the other table – that column is called the “foreign key”.
Can a table have multiple primary keys?
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. This article explains how and why to use primary keys. To set a table’s primary key, open the table in Design view.
Can we update foreign key in a table?
The foreign key relation can be created either through SSMS GUI or T-SQL. Rules for update/delete operations may be specified explicitly. However if nothing is specified then the default rule is No Action. The rule may be changed to any other option at any time later by recreating the FK relation.
How do you create a relationship between two tables in SQL?
Use SQL Server Management Studio
- In Object Explorer, right-click the table that will be on the foreign-key side of the relationship and select Design.
- From the Table Designer menu, select Relationships.
- In the Foreign-key Relationships dialog box, select Add.
- Select the relationship in the Selected Relationship list.
How can I have two foreign keys in SQL?
You can use the FOREIGN KEY REFERENCES constraint to implement a foreign key relationship in SQL Server. Specify the table name. Then specify in parenthesis the column name for the foreign key to reference it.
Why can a table have only one primary key?
The major reason is because that is the definition of the primary key. A table can have multiple unique keys that identify each row, but only one primary key. In databases such as MySQL, the primary key is also a clustered index. That provides a more direct reason.
Why does the referencing table have two foreign key columns?
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.
Can a foreign key be used as a primary key?
It is logically right in database management and in fact possible and must be allowed by any RDBMS to reference a foreign key to two or more tables that wants it’s primary key as a foreign key in a given table. It can be achievable with this example table structure below.
How can I add foreign keys to multiple tables?
You have a few options, all varying in “correctness” and ease of use. As always, the right design depends on your needs. You could simply create two columns in Ticket, OwnedByUserId and OwnedByGroupId, and have nullable Foreign Keys to each table.
Can a single column in a table reference multiple tables?
In SQL can a single column in a table reference multiple tables – no this is not possible. A foreign key always references one target table (and one table only).