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Answer: The FOREIGN KEY Constraint

Find a detailed explanation of how to set up a foreign key in a table.

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Solution

The solution is given below:

MySQL
/* Modifying the EmpID in the Skills table to be NOT NULL */
ALTER TABLE   Skills
MODIFY COLUMN EmpID INT NOT NULL;
/* Adding the foreign key constraint on EmpID in the Skills table */
ALTER TABLE     Skills
ADD FOREIGN KEY (EmpID) REFERENCES Employees (EmpID);
/* Describe the structure of the table */
DESC Skills;

Explanation

The explanation of the solution code is given below:

  • Lines 2–3: The ALTER TABLE statement makes changes in the structure of the Skills table. It modifies the EmpID column to be NOT NULL. A NULL value in this column can lead to orphaned rows, which can cause inconsistency and data integrity issues.

  • Lines 6–7: The ALTER TABLE statement makes changes in the structure of the Skills table. It sets the EmpID column in the ...