SQL Default Constraint Tutorial

Example Table

We will create a table named employees to demonstrate the SQL default constraint:

    CREATE TABLE employees (
        employee_id INT PRIMARY KEY,
        employee_name VARCHAR(100),
        hire_date DATE DEFAULT CURRENT_DATE,
        salary DECIMAL(10, 2) DEFAULT 50000.00
    );
    

Creating the Table

To create the table, use the following SQL command:

    CREATE TABLE employees (
        employee_id INT PRIMARY KEY,
        employee_name VARCHAR(100),
        hire_date DATE DEFAULT CURRENT_DATE,
        salary DECIMAL(10, 2) DEFAULT 50000.00
    );
    

Result:

Command	CREATE TABLE employees (employee_id INT PRIMARY KEY, employee_name VARCHAR(100), hire_date DATE DEFAULT CURRENT_DATE, salary DECIMAL(10, 2) DEFAULT 50000.00);
Result	A table named employees is created with default values for hire_date and salary.

Inserting Data into the Table

Let's insert some data into the employees table:

    INSERT INTO employees (employee_id, employee_name) VALUES
    (1, 'John Doe'),
    (2, 'Jane Smith'),
    (3, 'Alice Johnson');
    

Result:

Command	INSERT INTO employees (employee_id, employee_name) VALUES (1, 'John Doe'), (2, 'Jane Smith'), (3, 'Alice Johnson');
Result	Three records are inserted into the employees table with default values for hire_date and salary.

Querying the Table

We can query the employees table to see the data:

    SELECT * FROM employees;
    

Result:

Command	SELECT * FROM employees;
Result	employee_id employee_name hire_date salary 1 John Doe 2023-10-01 50000.00 2 Jane Smith 2023-10-01 50000.00 3 Alice Johnson 2023-10-01 50000.00