Contents
Can a column have multiple foreign keys?
Foreign Key Columns A single column can have multiple foreign key constraints. For an example, see Add multiple foreign key constraints to a single column.
How do I make multiple foreign keys in SQL?
3 Answers. The second code block from your question: ALTER TABLE ORDERS ADD FOREIGN KEY (customer_sid) REFERENCES CUSTOMER(SID), ADD FOREIGN KEY (customer_sid2) REFERENCES CUSTOMER(SID2); will take care of what you are trying to do.
Can a table have multiple unique keys?
A table can have more than one unique key unlike primary key. Unique key constraints can accept only one NULL value for column. Unique constraints are also referenced by the foreign key of another table.
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 a multi column foreign key stack?
Your problem is that you have id_chip with a foreign key to SIGNALS, and Signal_no with a foreign key to SIGNALS, both referencing a single column. Given that the PK on SIGNALS is a composite key, your FK on SIGNAL_RECEIVINGS needs to also be a composite to the table.
Can a foreign key be used as a primary key?
You could also put the information that is common for all users in one table and have separate tables for the information that is specific for the user types, so that you have a single table with user id as primary key. A foreign key can only reference a single primary key, so no. However, you could use a bridge table:
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.