Working with Intersection in MySQL

Intro

The INTERSECT operator allows us to join two queries together and only select the rows they share in common. This is similar to UNION except we only get rows that overlap. In this article, we will learn how to use the INTERSECT operator in MySQL.

The Syntax

The basic syntax of INTERSECT is as follows:

SELECT * [column_names] FROM [table]
INTERSECT
SELECT * [column_names] FROM [table2]

However, MySQL does not support intersect. We can accomplish the same result using the following.

SELECT DISTINCT [column_names]
FROM [table]
WHERE [column_names] IN 
  (SELECT [column_names] FROM [table2]);

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'),
(10001,62102,'1987-06-26','1988-06-25'),
(10001,66074,'1988-06-25','1989-06-25'),
(10001,66596,'1989-06-25','1990-06-25'),
(10001,66961,'1990-06-25','1991-06-25'),
(10001,71046,'1991-06-25','1992-06-24'),
(10001,74333,'1992-06-24','1993-06-24'),
(10001,75286,'1993-06-24','1994-06-24'),
(10001,75994,'1994-06-24','1995-06-24'),
(10001,76884,'1995-06-24','1996-06-23'),
(10001,80013,'1996-06-23','1997-06-23'),
(10001,81025,'1997-06-23','1998-06-23'),
(10001,81097,'1998-06-23','1999-06-23');

An Example

Let’s start with an example. Here we want to grab all employees who are born before 1962 and hired after 1982.

Since MySQL doesn't support INTERSECT, we have to use a sub query with the IN operator.

SELECT
	emp_no,
    first_name, 
    last_name,
    birth_date,
    hire_date 
FROM
    employees 
WHERE 
	birth_date < Date('1962-01-01')
AND emp_no IN (
	SELECT 
    	emp_no
	FROM
	    employees AS e2
	WHERE 
		e2.hire_date  > Date('1989-01-01')
);

emp_no	first_name	last_name	birth_date	hire_date
10005	Kyoichi	Maliniak	1955-01-21	1989-09-12
10006	Anneke	Preusig	1953-04-20	1989-06-02
10007	Tzvetan	Zielinski	1957-05-23	1989-02-10
10008	Saniya	Kalloufi	1958-02-19	1994-09-15
10011	Mary	Sluis	1953-11-07	1990-01-22
10012	Patricio	Bridgland	1960-10-04	1992-12-18
10016	Kazuhito	Cappelletti	1961-05-02	1995-01-27
10017	Cristinel	Bouloucos	1958-07-06	1993-08-03
10019	Lillian	Haddadi	1953-01-23	1999-04-30
10020	Mayuko	Warwick	1952-12-24	1991-01-26

Working with Intersection in MySQL

02.04.2022

Intro

The Syntax

Getting Setup

Creating a DB

An Example

Working with Union in Postgres

Working with Intersection in Postgres