The WHERE clause in SQL is used to filter records based on specific conditions. It allows you to retrieve only the rows that meet the specified criteria. The basic syntax of the WHERE clause is as follows:

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

Here, "condition" represents the condition or set of conditions that the data must satisfy for it to be included in the result set. You can use various comparison operators and logical operators in the condition to create complex filtering conditions.

Here are some examples to demonstrate the usage of the WHERE clause:

1. Retrieve records where the age is greater than 30:

sql
SELECT *
FROM employees
WHERE age > 30;

2. Retrieve records where the department is 'Sales' and the salary is greater than 5000:

sql
SELECT *
FROM employees
WHERE department = 'Sales' AND salary > 5000;

3. Retrieve records where the name starts with 'J' and the age is between 25 and 35:

sql
SELECT *
FROM employees
WHERE name LIKE 'J%' AND age BETWEEN 25 AND 35;

4. Retrieve records where the department is 'Marketing' or 'Finance':

sql
SELECT *
FROM employees
WHERE department = 'Marketing' OR department = 'Finance';

These are just a few examples of how you can use the WHERE clause to filter data in SQL. You can combine multiple conditions using logical operators like AND and OR to create more complex filtering conditions.