LEFT JOIN Keyword

I wanted to write a quick blog on LEFT JOIN because I get so many questions about this topic from young DB Admin’s and developers as well as Business Managers.

Define


In SQL the LEFT JOIN keyword will return all records from the left table (table a), and the matched records from the right table (table b). The result is NULL from the right side, if there is no match.

LEFT JOIN Syntax

SELECT column_names(s)
FROM table_a
LEFT JOIN table_b ON table_a.column_name = tableb.column_name

Instructional


In this instruction we will use two tables to demonstrate using LEFT JOIN within a SQL statement. Lets first define two database tables as well as include the data within those tables.

User table

Id Name Address Zip_Code
5 Bob Vance 45 Geear St 12345
6 Dwight Schrute 55 Sweet St 65565
7 Jim Halbret 65 Nice Rd 43455

Order Table

Id User_Id Employee_Id Order_Date
3 5 67 2019-01-01
45 15 89 2019-01-01
55 16 34 2019-01-01

Example


The following SQL statement will select all users, and any orders they might have.

SQL Demo

SELECT User.Name, Order.Id
FROM User
LEFT JOIN Order ON User.Id = Order.User_Id
ORDER BY User.Name DESC;

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