MySQL WHERE Clause

MySQL WHERE Clause

The MySQL WHERE clause is used to filter records. It is essential for querying specific rows in a table based on conditions.

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Syntax

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

The WHERE clause has the following components:

• column1, column2, ...: The columns to be retrieved.
• table_name: The name of the table from which to retrieve the data.
• condition: The condition to filter the records.

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Example MySQL WHERE Clause

Let's look at some examples of the MySQL WHERE clause:

Step 1: Using the Database

USE mydatabase;

This query sets the context to the database named mydatabase.

Step 2: Creating a Table

Create a table to work with:

CREATE TABLE employees (
    id INT AUTO_INCREMENT PRIMARY KEY,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL,
    email VARCHAR(100) UNIQUE,
    salary DECIMAL(10, 2)
);

This query creates a table named employees with columns for id, first_name, last_name, email, and salary.

Step 3: Inserting Initial Rows

Insert some initial rows into the table:

INSERT INTO employees (first_name, last_name, email, salary)
VALUES ('John', 'Doe', 'john.doe@example.com', 50000.00),
       ('Jane', 'Smith', 'jane.smith@example.com', 60000.00),
       ('Jim', 'Brown', 'jim.brown@example.com', 55000.00);

This query inserts three rows into the employees table.

Step 4: Using the WHERE Clause

Select rows based on a condition:

SELECT * 
FROM employees 
WHERE salary > 55000;

This query retrieves all columns from rows in the employees table where the salary is greater than 55000.

Step 5: Using Multiple Conditions

Select rows based on multiple conditions:

SELECT * 
FROM employees 
WHERE last_name = 'Doe' AND salary > 40000;

This query retrieves all columns from rows in the employees table where the last_name is 'Doe' and the salary is greater than 40000.

Step 6: Using the OR Operator

Select rows using the OR operator:

SELECT * 
FROM employees 
WHERE first_name = 'Jane' OR salary < 55000;

This query retrieves all columns from rows in the employees table where the first_name is 'Jane' or the salary is less than 55000.

Step 7: Using the BETWEEN Operator

Select rows using the BETWEEN operator:

SELECT * 
FROM employees 
WHERE salary BETWEEN 50000 AND 60000;

This query retrieves all columns from rows in the employees table where the salary is between 50000 and 60000.

Step 8: Using the IN Operator

Select rows using the IN operator:

SELECT * 
FROM employees 
WHERE last_name IN ('Doe', 'Smith');

This query retrieves all columns from rows in the employees table where the last_name is either 'Doe' or 'Smith'.

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Conclusion

The MySQL WHERE clause is a powerful tool for filtering records based on specific conditions. Understanding how to use the WHERE clause is essential for effective data querying and analysis in MySQL.