MySQL Practical Cheat Sheet for WordPress & Beginners (2026)

This guide includes the most useful real-world MySQL queries and backend connections you’ll actually need while working with WordPress or learning backend development.

1. Connect PHP to MySQL

$conn = new mysqli("localhost", "USERNAME", "PASSWORD", "DATABASE_NAME");

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
echo "Connected successfully!";

2. Basic SQL Queries (Core Commands)

Fetch Data

SELECT * FROM table_name;

Insert Data

INSERT INTO table_name (column1, column2)
VALUES ('value1', 'value2');

Update Data

UPDATE table_name
SET column1 = 'new_value'
WHERE id = 1;

Delete Data

DELETE FROM table_name
WHERE id = 1;

3. SQL Joins (Important)

INNER JOIN

SELECT users.name, comments.comment
FROM users
INNER JOIN comments
ON users.id = comments.user_id;

LEFT JOIN

SELECT users.name, comments.comment
FROM users
LEFT JOIN comments
ON users.id = comments.user_id;

4. Indexing (Performance)

Create Index

CREATE INDEX idx_name ON users(name);

Remove Index

DROP INDEX idx_name ON users;

5. WordPress Database Operations

 View Posts

SELECT * FROM wp_posts LIMIT 5;

Update Post Title

UPDATE wp_posts
SET post_title = 'New Title'
WHERE ID = 10;

Delete Spam Comments

DELETE FROM wp_comments
WHERE comment_content LIKE '%spam%';

Delete Trash Posts

DELETE FROM wp_posts
WHERE post_status = 'trash';

6. Reset WordPress Password

UPDATE wp_users
SET user_pass = MD5('newpassword')
WHERE user_login = 'admin';

7. Replace URLs (Very Useful)

UPDATE wp_posts
SET post_content = REPLACE(post_content, 'old-url', 'new-url');

 8. Fix Site URL (If Broken)

UPDATE wp_options
SET option_value = 'https://yourdomain.com'
WHERE option_name = 'siteurl';

UPDATE wp_options
SET option_value = 'https://yourdomain.com'
WHERE option_name = 'home';

9. Disable All Plugins (Emergency Fix)

UPDATE wp_options
SET option_value = 'a:0:{}'
WHERE option_name = 'active_plugins';

10. Secure Queries (Prevent SQL Injection)

Unsafe

$sql = "SELECT * FROM users WHERE username = '$input'";

 Safe (Prepared Statement)

$stmt = $conn->prepare("SELECT * FROM users WHERE username=?");
$stmt->bind_param("s", $username);
$stmt->execute();

11. Node.js + MySQL Connection

const mysql = require('mysql2');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  database: 'test'
});

connection.query('SELECT * FROM users', (err, results) => {
  console.log(results);
});

12. Important Safety Rules

• Always take a backup before running queries.

• Never run DELETE/UPDATE without WHERE

• Test queries on small data first

• Avoid editing core tables blindly.

• These are not just codes—they are your tools to control data.

 Start with small queries
 Practice in phpMyAdmin
 Apply to real problems (like spam comments, broken URLs)

That’s how you grow from beginner → professional.

Master data, and you master systems.