Basic CRUD Queries

Introduction

CRUD operations are the backbone of interacting with databases. CRUD stands for Create, Read, Update, and Delete. In MySQL, these operations allow users to manage and manipulate data within a database. This guide will provide detailed instructions and examples on how to perform these basic CRUD operations in MySQL.

Prerequisites

Before diving into CRUD operations, ensure you have:

• MySQL installed and running on your system.

• Basic understanding of SQL and relational database concepts.

• A MySQL database and a table to work with. For this guide, we'll use a simple table named employees in a database named company.

1. Create

Creating data involves inserting new records into a table. The INSERT statement is used for this purpose.

Example Table Structure

CREATE DATABASE company;

USE company;

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 NOT NULL,
    salary DECIMAL(10, 2) NOT NULL,
    hire_date DATE NOT NULL
);

Inserting Data

INSERT INTO employees (first_name, last_name, email, salary, hire_date) 
VALUES ('John', 'Doe', '[e-mail]', 50000.00, '2023-05-01');

You can insert multiple records in a single query:

INSERT INTO employees (first_name, last_name, email, salary, hire_date) 
VALUES 
('Jane', 'Smith', '[e-mail]', 55000.00, '2023-06-15'),
('Michael', 'Brown', '[e-mail]', 60000.00, '2023-07-20');

2. Read

Reading data from the database involves querying the table to retrieve records. The SELECT statement is used for this purpose.

Retrieving All Records

SELECT * FROM employees;

Retrieving Specific Columns

SELECT first_name, last_name, email FROM employees;

Retrieving Records with a Condition

SELECT * FROM employees WHERE salary > 55000;

Sorting Results

SELECT * FROM employees ORDER BY hire_date DESC;

3. Update

Updating data involves modifying existing records in a table. The UPDATE statement is used for this purpose.

Updating a Single Record

UPDATE employees 
SET salary = 65000 
WHERE email = '[e-mail]';

Updating Multiple Records

UPDATE employees 
SET salary = salary * 1.10 
WHERE hire_date < '2023-06-01';

4. Delete

Deleting data involves removing records from a table. The DELETE statement is used for this purpose.

Deleting a Single Record

DELETE FROM employees 
WHERE email = '[e-mail]';

Deleting Multiple Records

DELETE FROM employees 
WHERE salary < 55000;

Best Practices

• Backup Data: Always backup your data before performing DELETE or UPDATE operations.

• Use Transactions: For critical operations, use transactions to ensure data integrity.

• Test Queries: Test your queries on a small subset of data before applying them to the entire database.

• Use Constraints: Apply proper constraints like NOT NULL, UNIQUE, FOREIGN KEY to maintain data integrity.

Conclusion

Understanding and effectively using CRUD operations is essential for database management. By mastering CREATE, READ, UPDATE, and DELETE statements, you can efficiently interact with and manage your MySQL databases. Practice these operations regularly to become proficient in handling real-world database scenarios.