Working with Update Join in Postgres
03.08.2022
Intro
The UPDATE statement with the Join allows us to change rows in a table based on joined data. Often you will want to connect two tables and updated based on conditions form the joined result. In this article, we will learn how to use UPDATE Join in PostgreSql.
The Syntax
The basic syntax of UPDATE JOIN is as follows:
UPDATE [table_name]
JOIN [table2_name]
SET
column1 = value1,
column2 = value2
...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: 'postgres:latest'
ports:
- 5432:5432
environment:
POSTGRES_USER: username
POSTGRES_PASSWORD: password
POSTGRES_DB: default_database
volumes:
- psqldata:/var/lib/postgresql
phpmyadmin:
image: phpmyadmin/phpmyadmin
links:
- db
environment:
PMA_HOST: db
PMA_PORT: 3306
PMA_ARBITRARY: 1
restart: always
ports:
- 8081:80
volumes:
psqldata: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. If you don't understand these commands, don't worry, we will cover them in later articles.
We will be using the sample db provided here: https://dev.mysql.com/doc/sakila/en/. However, we will only enter what we need rather than import the whole db.
Next, let's create an film table. This is a slightly simplified version of the sakila database.
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 VARCHAR(1),
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');An Example
Let's start an example where we update an employee name. Notice that we use the WHERE clause to ensure we update the correct row.
UPDATE employees
JOIN salaries AS s ON employees.emp_no = s.emp_no
SET first_name = 'Alex',
last_name = 'Tam',
s.salary = 8000
WHERE s.salary < 70000;We often want to update only a single row or multiple rows based on a condition. However, it is worth noting that we can update all rows in the db if we leave off the WHERE clause.
This will update all employees and salaries.
UPDATE employees
JOIN salaries AS s ON employees.emp_no = s.emp_no
SET first_name = 'Alex',
last_name = 'Tam',
s.salary = 8000