Working with Delete Join in MySQL

Intro

The DELETE JOIN allows us to delete data from multiple tables using a join. Often we will want o connect multiple tables, then delete rows. In this article, we will learn how to use DELETE JOIN in MySQL.

The Syntax

The basic syntax of DELETE JOIN is as follows:

DELETE [table1], [table2]
FROM [table1]
JOIN [table2] ON key1 = key2
WHERE [condition]

This syntax will allow us to delete multiple rows based on the join and conditions we supply.

Getting Setup

We will be using docker in this article, but feel free to install your database locally instead. Once you have docker installed, create a new file called docker-compose.yml and add the following.

version: '3'
 
services:
  db:
    image: mysql:latest
    container_name: db
    environment:
      MYSQL_ROOT_PASSWORD: root_pass
      MYSQL_DATABASE: app_db
      MYSQL_USER: db_user
      MYSQL_PASSWORD: db_user_pass
    ports:
      - "6033:3306"
    volumes:
      - dbdata:/var/lib/mysql
  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    container_name: pma
    links:
      - db
    environment:
      PMA_HOST: db
      PMA_PORT: 3306
      PMA_ARBITRARY: 1
    restart: always
    ports:
      - 8081:80

volumes:
  dbdata:

Next, run docker-compose up.

Now, navigate to http://localhost:8081/ to access phpMyAdmin. Then log in with the username root and pass root_pass.

Click the SQL tab and you are ready to go.

Creating a DB

In this article, we will need some data to work with. We will be using the sample db provided here: https://dev.mysql.com/doc/employee/en/. However, we will only enter what we need rather than import the whole db.

With the SQL tab open (or your own sql cli going), let's first create our DB and select it.

create DATABASE if not EXISTS sakila;

USE sakila;

CREATE TABLE employees (
    emp_no      INT             NOT NULL,
    birth_date  DATE            NOT NULL,
    first_name  VARCHAR(14)     NOT NULL,
    last_name   VARCHAR(16)     NOT NULL,
    gender      ENUM ('M','F')  NOT NULL,    
    hire_date   DATE            NOT NULL,
    PRIMARY KEY (emp_no)
);

CREATE TABLE salaries (
    emp_no      INT             NOT NULL,
    salary      INT             NOT NULL,
    from_date   DATE            NOT NULL,
    to_date     DATE            NOT NULL,
    FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
    PRIMARY KEY (emp_no, from_date)
);

Now, let's enter a few rows

INSERT INTO employees VALUES (10001,'1953-09-02','Georgi','Facello','M','1986-06-26'),
(10002,'1964-06-02','Bezalel','Simmel','F','1985-11-21'),
(10003,'1959-12-03','Parto','Bamford','M','1986-08-28'),
(10004,'1954-05-01','Chirstian','Koblick','M','1986-12-01'),
(10005,'1955-01-21','Kyoichi','Maliniak','M','1989-09-12'),
(10006,'1953-04-20','Anneke','Preusig','F','1989-06-02'),
(10007,'1957-05-23','Tzvetan','Zielinski','F','1989-02-10'),
(10008,'1958-02-19','Saniya','Kalloufi','M','1994-09-15'),
(10009,'1952-04-19','Sumant','Peac','F','1985-02-18'),
(10010,'1963-06-01','Duangkaew','Piveteau','F','1989-08-24'),
(10011,'1953-11-07','Mary','Sluis','F','1990-01-22'),
(10012,'1960-10-04','Patricio','Bridgland','M','1992-12-18'),
(10013,'1963-06-07','Eberhardt','Terkki','M','1985-10-20'),
(10014,'1956-02-12','Berni','Genin','M','1987-03-11'),
(10015,'1959-08-19','Guoxiang','Nooteboom','M','1987-07-02'),
(10016,'1961-05-02','Kazuhito','Cappelletti','M','1995-01-27'),
(10017,'1958-07-06','Cristinel','Bouloucos','F','1993-08-03'),
(10018,'1954-06-19','Kazuhide','Peha','F','1987-04-03'),
(10019,'1953-01-23','Lillian','Haddadi','M','1999-04-30'),
(10020,'1952-12-24','Mayuko','Warwick','M','1991-01-26');

INSERT INTO salaries VALUES (10001,60117,'1986-06-26','1987-06-26'),
(10002,62102,'1987-06-26','1988-06-25'),
(10003,66074,'1988-06-25','1989-06-25'),
(10004,66596,'1989-06-25','1990-06-25'),
(10005,66961,'1990-06-25','1991-06-25'),
(10006,71046,'1991-06-25','1992-06-24'),
(10007,74333,'1992-06-24','1993-06-24'),
(10008,75286,'1993-06-24','1994-06-24'),
(10009,75994,'1994-06-24','1995-06-24'),
(10010,76884,'1995-06-24','1996-06-23'),
(10011,80013,'1996-06-23','1997-06-23'),
(10012,81025,'1997-06-23','1998-06-23'),
(10013,81097,'1998-06-23','1999-06-23');

Examples

Let’s do an example where we select multiple employees, joined with their salaries. We will filter based on salary then delete. This will remove all employee rows and salary rows that meet our search.

First, let’s select to see all the rows we will delete.

SELECT *
FROM employees AS e
	JOIN salaries AS s on e.emp_no = s.emp_no
WHERE s.salary < 70000;

emp_no	birth_date	first_name	last_name	gender	hire_date	emp_no	salary	from_date	to_date
10001	1953-09-02	Georgi	Facello	M	1986-06-26	10001	60117	1986-06-26	1987-06-26
10001	1953-09-02	Georgi	Facello	M	1986-06-26	10001	62102	1987-06-26	1988-06-25
10001	1953-09-02	Georgi	Facello	M	1986-06-26	10001	66074	1988-06-25	1989-06-25
10001	1953-09-02	Georgi	Facello	M	1986-06-26	10001	66596	1989-06-25	1990-06-25
10001	1953-09-02	Georgi	Facello	M	1986-06-26	10001	66961	1990-06-25	1991-06-25

DELETE employees
	FROM employees
	JOIN salaries AS s on employees.emp_no = s.emp_no
WHERE s.salary < 70000;

Since we specify employee after DELETE this will delete the employee rows based on our join condition. On thing to notice is we have ON DELETE CASCADE on the salary table, thus when we delete the linked employee, the salary row will also be deleted.

SELECT * FROM salaries s;

emp_no	salary	from_date	to_date
10006	71046	1991-06-25	1992-06-24
10007	74333	1992-06-24	1993-06-24
10008	75286	1993-06-24	1994-06-24
10009	75994	1994-06-24	1995-06-24
10010	76884	1995-06-24	1996-06-23
10011	80013	1996-06-23	1997-06-23
10012	81025	1997-06-23	1998-06-23
10013	81097	1998-06-23	1999-06-23

Working with Delete Join in MySQL

03.01.2022

Intro

The Syntax

Getting Setup

Creating a DB

Examples

Working with Delete Cascade in Postgres

Working with Delete Join in Postgres