5.4. FOREIGN KEY


  •  A FOREIGN KEY is a key used to link two tables together.
  • A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
  • The table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table.

QUERY: - create table tbname (column_name datatype References parent_table(primary column name));

EXAMPLE: - create table salary (salary int references employee (e_id));

  • SQL FOREIGN KEY on ALTER TABLE:-

QUERY: - ALTER TABLE Table_name ADD FOREIGN KEY (column) REFERENCES diff_table_name (column);

EXAMPLE: - ALTER TABLE salary ADD FOREIGN KEY (salary) REFERENCES employee (e_id);


Last modified: Monday, 2 December 2019, 12:18 PM