Exploring IS NULL and IS NOT NULL Operators in MySQL Workbench

• In MySQL Workbench, the `IS NULL` and `IS NOT NULL` operators are used to filter data based on whether a column's value is NULL or not NULL, respectively. NULL represents the absence of a value in a column, and these operators help you identify and handle such cases.

Here's a detailed explanation of how `IS NULL` and `IS NOT NULL` work, along with examples:

    SELECT columns

    FROM table

    WHERE column IS NULL;

    SELECT columns

    FROM table

    WHERE column IS NOT NULL;

• Consider a "employees" table with the following data:

    CREATE TABLE employees (

        employee_id INT PRIMARY KEY,

        first_name VARCHAR(50),

        last_name VARCHAR(50),

        hire_date DATE

    );

 

    INSERT INTO employees (employee_id, first_name, last_name, hire_date)

    VALUES

        (1, 'John', 'Smith', '2023-01-15'),

        (2, 'Jane', 'Doe', NULL),

        (3, 'Michael', 'Johnson', '2023-02-20'),

        (4, 'Emily', 'Brown', NULL),

        (5, 'David', 'Lee', '2023-03-10');

• Using IS NULL: To retrieve rows where a column's value is NULL:

    SELECT * FROM employees WHERE hire_date IS NULL;

• This query would return rows where the `hire_date` is NULL, i.e., rows 2 and 4.

• Using IS NOT NULL: To retrieve rows where a column's value is not NULL:

    SELECT * FROM employees WHERE hire_date IS NOT NULL;

• This query would return rows where the `hire_date` is not NULL, i.e., rows 1, 3, and 5.

• Using IS NULL with Multiple Conditions: You can use `IS NULL` and `IS NOT NULL` along with other conditions in the `WHERE` clause.

    SELECT * FROM employees WHERE hire_date IS NULL AND first_name = 'Jane';

• This query would return the row where `hire_date` is NULL and `first_name` is 'Jane'.

• Using IS NULL in JOINs: You can use `IS NULL` to identify rows with missing related data in a joined table.

    SELECT customers.customer_id, orders.order_id

    FROM customers

    LEFT JOIN orders ON customers.customer_id = orders.customer_id

    WHERE orders.order_id IS NULL;

• This query would return customer IDs that have no associated orders.

• The `IS NULL` and `IS NOT NULL` operators are essential for handling missing or unknown data in your database. They help you identify rows where certain columns lack values, which can be crucial for data validation and analysis.