How to use LEFT in Sql Server

Intro

The left function provides a way to retrieve the first n (number you specify) characters from a string. One often use of this function is to extract dates from a string, although SQL Server does provide some better functions for getting dates. In this article, we will learn how to use left with SQL Server.

The Syntax

The basic syntax of a LEFT is as follows:

SELECT LEFT(string, n);

• n: The number of characters you would like to extract.

Getting Setup

For this, we will be using docker. This is recommended for more than just using SQL Server. To find how to install docker go here: https://docs.docker.com/engine/install/

Now create a file called docker-compose.yml and add the following.

version: "3.9"
services:
  db:
    image: "mcr.microsoft.com/mssql/server"
    ports: 
      - 1433:1433
    environment:
        SA_PASSWORD: "Your_password123"
        ACCEPT_EULA: "Y"

Open a terminal and go to the folder the file is located. Then run the following.

docker-compose up

If you are looking for another good reference, you can check here: https://docs.docker.com/samples/aspnet-mssql-compose/.

Basic Example

Let's try this on a table. We can create an employee table and insert some rows.

CREATE TABLE employees (
    first_name VARCHAR (50) NOT NULL,
    last_name VARCHAR (50) NOT NULL,
);

insert into employees (first_name, last_name) 
	values 
	('keith', 'holliday'),
	('jon', 'doe'),
	('jon', 'dane'),
	('jane', 'done'),
	('anna', 'smith');

Below is an example of extracting the first 3 characters from each of the employees last name. This could be use to construct a unique id or an email.

select 
	left(last_name, 3) as LastName
from employees e;