MySQL Cheat Sheet

Help with SQL commands to interact with a MySQL database

MySQL Locations

Mac /usr/local/mysql/bin
Windows /Program Files/MySQL/MySQL version/bin
Xampp /xampp/mysql/bin

Add mysql to your PATH

# Current Session
export PATH=${PATH}:/usr/local/mysql/bin
# Permanantly
echo 'export PATH="/usr/local/mysql/bin:$PATH"' >> ~/.bash_profile

On Windows - https://www.qualitestgroup.com/resources/knowledge-center/how-to-guide/add-mysql-path-windows/

Login

mysql -u root -p

Show Users

SELECT User, Host FROM mysql.user;

Create User

CREATE USER 'someuser'@'localhost' IDENTIFIED BY 'somepassword';

Grant All Priveleges On All Databases

GRANT ALL PRIVILEGES ON * . * TO 'someuser'@'localhost';
FLUSH PRIVILEGES;

Show Grants

SHOW GRANTS FOR 'someuser'@'localhost';

Remove Grants

REVOKE ALL PRIVILEGES, GRANT OPTION FROM 'someuser'@'localhost';

Delete User

DROP USER 'someuser'@'localhost';

Exit

exit;

Show Databases

SHOW DATABASES

Create Database

CREATE DATABASE acme;

Delete Database

DROP DATABASE acme;

Select Database

USE acme;

Create Table

CREATE TABLE users(
id INT AUTO_INCREMENT,
   first_name VARCHAR(100),
   last_name VARCHAR(100),
   email VARCHAR(50),
   password VARCHAR(20),
   location VARCHAR(100),
   dept VARCHAR(100),
   is_admin TINYINT(1),
   register_date DATETIME,
   PRIMARY KEY(id)
);

Delete / Drop Table

DROP TABLE tablename;

Show Tables

SHOW TABLES;

Insert Row / Record

INSERT INTO users (first_name, last_name, email, password, location, dept, is_admin, register_date) values ('Brad', 'Traversy', '[email protected]', '123456','Massachusetts', 'development', 1, now());

Insert Multiple Rows

INSERT INTO users (first_name, last_name, email, password, location, dept,  is_admin, register_date) values ('Fred', 'Smith', '[email protected]', '123456', 'New York', 'design', 0, now()), ('Sara', 'Watson', '[email protected]', '123456', 'New York', 'design', 0, now()),('Will', 'Jackson', '[email protected]', '123456', 'Rhode Island', 'development', 1, now()),('Paula', 'Johnson', '[email protected]', '123456', 'Massachusetts', 'sales', 0, now()),('Tom', 'Spears', '[email protected]', '123456', 'Massachusetts', 'sales', 0, now());

Select

SELECT * FROM users;
SELECT first_name, last_name FROM users;

Where Clause

SELECT * FROM users WHERE location='Massachusetts';
SELECT * FROM users WHERE location='Massachusetts' AND dept='sales';
SELECT * FROM users WHERE is_admin = 1;
SELECT * FROM users WHERE is_admin > 0;

Delete Row

DELETE FROM users WHERE id = 6;

Update Row

UPDATE users SET email = '[email protected]' WHERE id = 2;

Add New Column

ALTER TABLE users ADD age VARCHAR(3);

Modify Column

ALTER TABLE users MODIFY COLUMN age INT(3);

Order By (Sort)

SELECT * FROM users ORDER BY last_name ASC;
SELECT * FROM users ORDER BY last_name DESC;

Concatenate Columns

SELECT CONCAT(first_name, ' ', last_name) AS 'Name', dept FROM users;

Select Distinct Rows

SELECT DISTINCT location FROM users;

Between (Select Range)

SELECT * FROM users WHERE age BETWEEN 20 AND 25;

Like (Searching)

SELECT * FROM users WHERE dept LIKE 'd%';
SELECT * FROM users WHERE dept LIKE 'dev%';
SELECT * FROM users WHERE dept LIKE '%t';
SELECT * FROM users WHERE dept LIKE '%e%';

Not Like

SELECT * FROM users WHERE dept NOT LIKE 'd%';

IN

SELECT * FROM users WHERE dept IN ('design', 'sales');

Create & Remove Index

CREATE INDEX LIndex On users(location);
DROP INDEX LIndex ON users;

New Table With Foreign Key (Posts)

CREATE TABLE posts(
id INT AUTO_INCREMENT,
   user_id INT,
   title VARCHAR(100),
   body TEXT,
   publish_date DATETIME DEFAULT CURRENT_TIMESTAMP,
   PRIMARY KEY(id),
   FOREIGN KEY (user_id) REFERENCES users(id)
);

Add Data to Posts Table

INSERT INTO posts(user_id, title, body) VALUES (1, 'Post One', 'This is post one'),(3, 'Post Two', 'This is post two'),(1, 'Post Three', 'This is post three'),(2, 'Post Four', 'This is post four'),(5, 'Post Five', 'This is post five'),(4, 'Post Six', 'This is post six'),(2, 'Post Seven', 'This is post seven'),(1, 'Post Eight', 'This is post eight'),(3, 'Post Nine', 'This is post none'),(4, 'Post Ten', 'This is post ten');

INNER JOIN

SELECT
  users.first_name,
  users.last_name,
  posts.title,
  posts.publish_date
FROM users
INNER JOIN posts
ON users.id = posts.user_id
ORDER BY posts.title;

New Table With 2 Foriegn Keys

CREATE TABLE comments(
	id INT AUTO_INCREMENT,
    post_id INT,
    user_id INT,
    body TEXT,
    publish_date DATETIME DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY(id),
    FOREIGN KEY(user_id) references users(id),
    FOREIGN KEY(post_id) references posts(id)
);

Add Data to Comments Table

INSERT INTO comments(post_id, user_id, body) VALUES (1, 3, 'This is comment one'),(2, 1, 'This is comment two'),(5, 3, 'This is comment three'),(2, 4, 'This is comment four'),(1, 2, 'This is comment five'),(3, 1, 'This is comment six'),(3, 2, 'This is comment six'),(5, 4, 'This is comment seven'),(2, 3, 'This is comment seven');

Left Join

SELECT
comments.body,
posts.title
FROM comments
LEFT JOIN posts ON posts.id = comments.post_id
ORDER BY posts.title;

Join Multiple Tables

SELECT
comments.body,
posts.title,
users.first_name,
users.last_name
FROM comments
INNER JOIN posts on posts.id = comments.post_id
INNER JOIN users on users.id = comments.user_id
ORDER BY posts.title;

Aggregate Functions

SELECT COUNT(id) FROM users;
SELECT MAX(age) FROM users;
SELECT MIN(age) FROM users;
SELECT SUM(age) FROM users;
SELECT UCASE(first_name), LCASE(last_name) FROM users;

Group By

SELECT age, COUNT(age) FROM users GROUP BY age;
SELECT age, COUNT(age) FROM users WHERE age > 20 GROUP BY age;
SELECT age, COUNT(age) FROM users GROUP BY age HAVING count(age) >=2;

如果在使用MySQL删除一个大表的数据时没有反应，可能是由于删除操作需要很长时间，MySQL卡在了执行操作的状态。此时，您可以尝试以下步骤：

检查MySQL服务器的磁盘空间和内存使用情况，确保有足够的空间和内存资源来执行删除操作。

检查当前是否有其他MySQL操作正在执行，如查询或更新，这些操作可能会占用MySQL服务器的资源，导致删除操作无法完成。您可以使用SHOW PROCESSLIST;命令查看当前正在运行的MySQL进程列表。

尝试使用KILL命令终止当前正在运行的MySQL进程，以释放资源。例如，KILL [进程ID];命令可以终止指定进程。

如果删除操作仍然无法完成，您可以尝试使用MySQL的TRUNCATE命令来清空整个表。这比使用DELETE命令删除数据要快得多，因为它只是删除表中的所有行，而不是逐行删除。

如果您仍然无法删除表中的数据，请考虑使用外部工具，如mysqldump和mysqlimport来备份和恢复表数据。将表导出到一个文件中，然后删除整个表，并将备份数据重新导入到表中。

注意：在执行上述任何操作之前，请务必备份您的数据库和表数据，以防止意外数据损失。

您可以使用MySQL的KILL命令来终止MySQL中的进程。以下是具体步骤：

打开MySQL客户端，连接到您的MySQL服务器。

运行SHOW PROCESSLIST;命令，以查看当前正在运行的MySQL进程列表。

找到您想要终止的进程的ID。在Id列中查找该进程的ID号。

运行KILL [进程ID];命令，以终止该进程。将[进程ID]替换为您要终止的进程的实际ID号。例如，KILL 1234;命令可以终止ID为1234的进程。

请注意，终止MySQL进程会立即停止该进程的执行，因此请确保您要终止的进程是正确的，并且不会对数据库的完整性或可用性产生负面影响。

sxfmol/mysql_cheat_sheet.md