SQL NOT NULL Constraint
SQL NOT NULL Constraint
In SQL, the NOT NULL constraint is used to ensure that a column cannot contain NULL values. When we define a column with the NOT NULL constraint, it means that it is mandatory to provide a value for that column for every row in the table. If we try to insert a row with a NULL value in a column with the NOT NULL constraint, the database will return an error.
Here is an example of how to define a column with the NOT NULL constraint:
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(50) NOT NULL,
email VARCHAR(50) NOT NULL,
phone VARCHAR(20)
);
In this example, we have defined a table called “employees” with four columns: “id”, “name”, “email”, and “phone”. The “id” column is the primary key of the table, while the “name” and “email” columns have the NOT NULL constraint, which means that they cannot contain NULL values.
Here is an example of how to insert data into the “employees” table with the NOT NULL constraint:
INSERT INTO employees (id, name, email, phone)
VALUES (1, 'John Doe', 'johndoe@email.com', '123-456-7890');
In this example, we are inserting a new row into the “employees” table with values for the “id”, “name”, “email”, and “phone” columns. Since the “name” and “email” columns have the NOT NULL constraint, we must provide values for those columns in the INSERT statement.
In summary, the NOT NULL constraint is used to ensure that a column cannot contain NULL values in SQL. It is essential for maintaining data integrity and ensuring the accuracy and consistency of data in a database.