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Answer: The UNIQUE Constraint

Find a detailed explanation of how to use the UNIQUE constraint on columns of an existing table.

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Solution

The solution is given below:

MySQL
/* Applying UNIQUE contraint on EmpName */
ALTER TABLE Employees ADD UNIQUE (EmpName);
/* Inserting a new record in the table */
INSERT INTO Employees VALUES (5, 'Susan Lee', 5000);
/* Retrieve the records in the table */
SELECT * FROM Employees;

Explanation

The explanation of the solution code is given below:

  • Line 2: The ALTER TABLE query modifies a table. ADD is used to add a constraint. UNIQUE takes in a column name as a parameter and applies a unique constraint on that column.

  • Line 5: The INSERT INTO statement is followed by the table name, Employees, which will be modified. The VALUES clause specifies the values.

  • Line ...