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Understanding the AND Keyword

SQL (Structured Query Language) is a powerful tool for managing and manipulating relational databases. One of the fundamental aspects of SQL is the ability to filter data based on certain conditions. The AND keyword is crucial for combining multiple conditions in SQL queries. In this tutorial, we’ll explore how to use the AND keyword effectively to refine our queries.

1. Understanding the AND Keyword
   The AND keyword is used to combine multiple conditions in a SQL query. When using AND, all conditions must be true for a row to be included in the result set.
2. Syntax:
   The basic syntax of using AND in a SQL query is as follows:

   SELECT column1, column2, ...
   FROM table_name
   WHERE condition1 AND condition2 AND ...;

3. Example Scenario:
   Let’s consider a scenario where we have a table named employees with columns employee_id, first_name, last_name, and department. We want to retrieve all employees who work in the ‘Marketing’ department and have a salary greater than $50,000.
4. Creating Sample Data:
   Before we proceed, let’s create some sample data to work with:

   CREATE TABLE employees (
       employee_id INT PRIMARY KEY,
       first_name VARCHAR(50),
       last_name VARCHAR(50),
       department VARCHAR(50),
       salary DECIMAL(10, 2)
   );

   INSERT INTO employees (employee_id, first_name, last_name, department, salary)
   VALUES
       (1, 'John', 'Doe', 'Marketing', 60000),
       (2, 'Jane', 'Smith', 'Marketing', 55000),
       (3, 'Alice', 'Johnson', 'HR', 48000),
       (4, 'Bob', 'Brown', 'IT', 70000);

5. Using the AND Keyword in a Query:
   Now, let’s write a SQL query to retrieve employees who work in the ‘Marketing’ department and have a salary greater than $50,000:

   SELECT first_name, last_name
   FROM employees
   WHERE department = 'Marketing' AND salary > 50000;

6. Explanation:

• SELECT: Specifies the columns we want to retrieve (first_name and last_name).
• FROM: Specifies the table from which to retrieve data (employees table).
• WHERE: Specifies the conditions that must be met for a row to be included in the result set.
• department = 'Marketing': This condition ensures that only employees from the ‘Marketing’ department are included.
• salary > 50000: This condition ensures that only employees with a salary greater than $50,000 are included.

6. Expected Output:
   The query will return the following result:

   | first_name | last_name |
   |------------|-----------|
   | John       | Doe       |
   | Jane       | Smith     |

Conclusion

In this tutorial, we’ve learned how to use the AND keyword to combine multiple conditions in SQL queries. By combining conditions using AND, we can precisely filter data based on our requirements.

By following these steps and examples, you should now have a solid understanding of how to use the AND keyword in SQL queries. Practice writing your own queries to reinforce your understanding.