Working with Concat in Postgres

Intro

Postgresql provides a few ways to concatenate strings. We can use the concat operator, ||. We also have the CONCAT and CONCAT_WS function. In this article, we will learn how to concatenate strings in Postgresql.

The Syntax

The basic syntax of a CONCAT is as follows:

SELECT CONCAT(string1, string2, ...more_strings);

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)
);

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');

The CONCAT Operator ||

The first way we can concat strings is using the ||. Let's use this to build full names for our employees.

select 
	first_name || ' ' || last_name as full_name
from employees e ;

The CONCAT function

We can accomplish the same using the CONCAT function.

select 
	CONCAT(first_name, ' ', last_name) as full_name
from employees e ;

The CONCAT_WS function

We can accomplish the same using the CONCAT_WS function, but this function also provides more. We can specify a separator then a list of strings. The prevents us from having to type our separate multiple times.

To get a sense of this, let's also add in the birth date to concatenate. We will use a space as the separator. Notice, in the previous example, we would have needed to type space multiple times.

select 
	CONCAT_WS(' ', first_name, last_name, birth_date) as full_name_and_date
from employees e;