Can I have 2 foreign keys to the same 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 row be primary and foreign key?
You ‘ll find the answer into this link: Can a database attribute be primary and foreign key? You can create a column having both keys (primary and foreign) but then it will be one to one mapping and add uniqueness to this column.
Can Unique Key have duplicate values?
A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values.
How to define foreign key referencing two columns?
If the Primary Key you are referencing is specified as (Application, ID) then your foreign key must reference (Application, ID) and NOT (ID, Application) as they are seen as two different keys. the column order on table A should be –> A_ID then A_Name; defining the foreign key should follow the same order as well.
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.
When to use foreign key in table library?
If your field Application in table Library has a foreign key that references a field in another table (named Application I would bet), then your field Application in table Library has to have a foreign key to table Application too. After that you can do your composed foreign key.
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.