Working with Truncate Table in Postgres
03.29.2022
Intro
The Truncate Table allows us to delete large tables quickly. If you want to delete all records, the DELETE command will be slower than TRUNCATE. This is because TRUNCATE will skip many checks that are normally performed. In this article, we will learn how to use TRUNCATE in Postgresql.
The Syntax
The basic syntax of Truncate Table is as follows:
TRUNCATE TABLE [table_name]
[PARAMETER]Truncate table has the following parameter options.
- CASCADE: this will delete all things and foren-keys
- RESTART IDENTITY: Restarts orders owned by columns of the truncated tables
- CONTINUE IDENTITY: Default option. Does not change the values of orders
- RESTRICT: Also default. Will decline if other tables have foreign-key references
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');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');An Example
To truncate a single table, we can run the following.
TRUNCATE TABLE employees;If your table has records with foreign key references, you can use the CASCADE command.
TRUNCATE TABLE employees CASCADE;And finally, we can truncate multiple tables at once using the following.
TRUNCATE TABLE employees, salaries;