What is a foreign key in a relation what is its use?
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
How can you identify a foreign key relationship?
To see foreign key relationships of a column: SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA. KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_SCHEMA = ‘db_name’ AND REFERENCED_TABLE_NAME = ‘table_name’ AND REFERENCED_COLUMN_NAME = ‘column_name’;
Where is foreign key in relational schema?
Foreign keys in a table are indicated by drawing a line to the corresponding primary key in the table from which it originates – you can also add “(FK)” to the key to further highlight that it is a foreign key.
Why do we need foreign keys in a relational database?
The FOREIGN KEY constraint is crucial to relational database design. It lets us link the data according to our needs. As it creates some dependencies between the columns of primary and foreign tables, it also lets us decide what to do ON UPDATE and ON DELETE actions performed on the rows of the primary table.
How is foreign key related to primary key?
A foreign key is a column or a set of columns in one table that references the primary key columns in another table. The primary key is defined as a column (or set of columns) where each value is unique and identifies a single row of the table.
Which table does foreign key belong to?
Using SQL Server Management Studio
- Open the Table Designer for the table containing the foreign key you want to view, right-click in the Table Designer, and choose Relationships from the shortcut menu.
- In the Foreign Key Relationships dialog box, select the relationship with properties you want to view.
What are foreign key constraint?
A foreign key constraint specifies that the key can only contain values that are in the referenced primary key, and thus ensures the referential integrity of data that is joined on the two keys. You can identify a table’s foreign key when you create the table, or in an existing table with ALTER TABLE .
How can you identify a foreign key in a table in SQL?