Home Next Previous SQL ALTER Statement ADD FOREIGN KEY The ALTER Statement is used to add a new constraint to an existing table. Add Foreign Key Constraint Syntax: ALTER TABLE table_name ADD CONSTRAINT ConstraintName FOREIGN KEY (column_name) REFERENCES table_name(column_name); Example: Objective: In this example, we will add a foreign key constraint to an existing table project. ALTER TABLE Tbl_Emp ADD CONSTRAINT fk_const FOREIGN KEY (column_name) REFERENCES table_name(column_name);