MYSQL Tutorial

MySQL WHERE Clause – Filter Data Like a Pro

The WHERE clause is used to filter records in SQL based on one or more conditions. It is often combined with SELECT, UPDATE, DELETE, and other commands.

🔹 Basic Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition;
  

🔹 Example Table: employees

Let’s use this sample table again:

| employee_id | first_name | last_name | department | salary | hire_date  |
|-------------|------------|-----------|------------|--------|------------|
| 1           | John       | Doe       | Sales      | 50000  | 2020-01-10 |
| 2           | Jane       | Smith     | Marketing  | 60000  | 2019-05-15 |
| 3           | Mike       | Johnson   | IT         | 70000  | 2021-03-01 |
  

🔹 Example 1: Filter by One Condition

Get employees from the Sales department:

SELECT * FROM employees WHERE department = 'Sales';
  

🔹 Example 2: Numeric Comparison

Get employees with salary greater than 55,000:

SELECT first_name, salary FROM employees WHERE salary > 55000;
  

🔹 Example 3: Multiple Conditions with AND

Get employees from the IT department and salary above 60,000:

SELECT * FROM employees WHERE department = 'IT' AND salary > 60000;
  

🔹 Example 4: Multiple Conditions with OR

Get employees from Sales or Marketing departments:

SELECT * FROM employees WHERE department = 'Sales' OR department = 'Marketing';
  

🔹 Example 5: Using IN for Multiple Values

Another way to write example 4 using IN:

SELECT * FROM employees WHERE department IN ('Sales', 'Marketing');
  

🔹 Example 6: Filtering by Date

Get employees hired after January 1, 2020:

SELECT * FROM employees WHERE hire_date > '2020-01-01';
  

🔹 Interactive Challenge

Write a query to find employees who earn less than 60,000 and are in the Marketing department.

SELECT * FROM employees WHERE salary < 60000 AND department = 'Marketing';
    

🔹 Summary

• WHERE filters rows based on conditions.
• Use =, <, >, <=, >=, <> for comparisons.
• Combine conditions with AND and OR.
• Use IN to test for multiple values.
• Works with numbers, text, and dates.