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(The data type of the Foreign Key must match the datatype of the referenced key.)

The Foreign Key constraint on the column Dept_Code allows values only if they already exist in the
referenced table, Department. This means that if you try to insert the following values:

INSERT INTO Programming_Courses Values ('CS300', 'FDB-DB001', 'Database Systems');

the database will raise a Foreign Key violation error, because CS300 does not exist in the Department
table. But when you try a key value that exists:

INSERT INTO Programming_Courses VALUES ('CS205', 'FDB-DB001', 'Database Systems');
INSERT INTO Programming_Courses VALUES ('CS205', 'DB2-DB002', 'Database Systems II');

then the database allows these values.

A few tips for using Foreign Keys

• A Foreign Key must reference a UNIQUE (or PRIMARY) key in the parent table.
• Entering a NULL value in a Foreign Key column does not raise an error.
• Foreign Key constraints can reference tables within the same database.
• Foreign Key constraints can refer to another column in the same table (self-reference).

Read Foreign Keys online: https://riptutorial.com/sql/topic/1533/foreign-keys

https://riptutorial.com/ 65