Working with Replace in MySQL

03.04.2022

Intro

The REPLACE statement allows us to overwrite a new row when we insert. When using REPLACE, MySQL will delete a row if there is a duplicate, then insert the new row. In this article, we will learn how to use REPLACE in MySQL.

The Syntax

The basic syntax of REPLACE is as follows:

REPLACE INOT [table]([columns])
VALUES([values]);

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 of Replace Insert

Let’s start by inserting some data:

INSERT INTO employees VALUES 
(10001,'1953-09-02','Georgi','Facello','M','1986-06-26'),
(10002,'1964-06-02','Bezalel','Simmel','F','1985-11-21');

Now, let’s select the rows to see the ids.

SELECT * FROM employees;
emp_no birth_date first_name last_name gender hire_date
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

If we want to replace row 2, we can insert using the following.

REPLACE INTO employees(emp_no, birth_date, first_name, last_name, gender, hire_date) 
VALUES (10002,'1953-01-23','Lillian','Haddadi','M','1999-04-30');

Now, select the data again.

SELECT * FROM employees;
emp_no birth_date first_name last_name gender hire_date
10002 1953-01-23 Lillian Haddadi M 1999-04-30
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

Notice that there was a conflict on the emp_no key, so the full row was replaced.

Replace Updates

We can also use REPLACE to update our data. The REPLACE works like an UPDATE, except we don’t need to use the WHERE clause as REPLACE will search for a matching record first. For example, we can update row 3, like so:

REPLACE INTO employees
SET emp_no = 1003,
	birth_date = '1953-01-23',
    first_name = 'Alex',
    last_name = 'Tam',
    gender = 'M',
   	hire_date = '1999-04-30';

And the result:

SELECT * FROM employees;
emp_no birth_date first_name last_name gender hire_date
10002 1953-01-23 Lillian Haddadi M 1999-04-30
10003 1953-01-23 Alex Tam M 1999-04-30