Foreign keys connect data from one table to data from another. To develop a manner of cross-referencing the two columns, a foreign key column in one table leads to a column with unique values in another table (typically the primary key column).
A foreign key is a column (or set of columns) in a table whose values must match those of another table's column. Referential integrity is enforced by FOREIGN KEY restrictions, which states that if column value A refers to column value B, then column value B must exist.
The term "foreign key" refers to a database key that connects two tables. By referencing a column, or group of columns, in the Child table that includes the foreign key to the PRIMARY KEY column or set of columns in the Parent table, the FOREIGN KEY constraint identifies the links between database tables.
The FOREIGN KEY constraint is used to prevent activities from destroying table linkages. A FOREIGN KEY is a field (or set of fields) in one table that refers to the PRIMARY KEY in a different table.
In relational database design, the FOREIGN KEY constraint is critical. It allows us to link data based on our requirements. It also helps us determine what to do with ON UPDATE and ON DELETE actions done on the rows of the primary table because it introduces certain dependencies between the columns of the primary and foreign tables.