What is a foreign key and what is it used for?

What is a foreign key and why are they used?

A Foreign Key is a database key that is used to link two tables together. The FOREIGN KEY constraint identifies the relationships between the database tables by referencing a column, or set of columns, in the Child table that contains the foreign key, to the PRIMARY KEY column or set of columns, in the Parent table.

What is foreign key explain with an example?

A foreign key is a set of attributes in a table that refers to the primary key of another table. The foreign key links these two tables. … For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table.

What’s a foreign key in a database?

Foreign keys. A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table. In order to add a row with a given foreign key value, there must exist a row in the related table with the same primary key value.

What is a foreign key used for?

A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables to control the data that can be stored in the foreign key table.

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Why do we use foreign keys?

Foreign keys link data in one table to the data in another table. A foreign key column in a table points to a column with unique values in another table (often the primary key column) to create a way of cross-referencing the two tables.

Why foreign key constraint is important?

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 do foreign keys work?

A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.

Are foreign keys necessary?

24 Answers. Foreign keys help enforce referential integrity at the data level. They also improve performance because they’re normally indexed by default. If you need an index create one, this should not be a primary reason for FKs.

Is a foreign key a primary key?

Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table.

Where does the foreign key go?

The table that contains the foreign key is considered the child table, and the table that the foreign key references is the parent table.

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