Editing Join (SQL) (section)

==Example tables==
To explain join types, the rest of this article uses the following tables:
{| class="wikitable" style="text-align:center; float:left; margin-right:5px"
|+Employee table
|-
! LastName !! DepartmentID
|-
| Rafferty ||31
|-
| Jones || 33
|-
| Heisenberg || 33
|-
| Robinson || 34
|-
| Smith|| 34
|-
| Williams || {{null result}}
|}

{| class="wikitable" style="text-align:center; float:left; margin-left:5px"
|+Department table
|-
! DepartmentID !! DepartmentName
|-
| 31 || Sales
|-
| 33 || Engineering
|-
| 34 || Clerical
|-
| 35 || Marketing
|}

{{clear}}

<code>Department.DepartmentID</code> is the [[primary key]] of the <code>Department</code> table, whereas <code>Employee.DepartmentID</code> is a [[foreign key]].

Note that in <code>Employee</code>, "Williams" has not yet been assigned to a department. Also, no employees have been assigned to the "Marketing" department.

These are the SQL statements to create the above tables:

<syntaxhighlight lang="sql" line="1">
CREATE TABLE department(
    DepartmentID INT PRIMARY KEY NOT NULL,
    DepartmentName VARCHAR(20)
);

CREATE TABLE employee (
    LastName VARCHAR(20),
    DepartmentID INT REFERENCES department(DepartmentID)
);

INSERT INTO department
VALUES (31, 'Sales'),
       (33, 'Engineering'),
       (34, 'Clerical'),
       (35, 'Marketing');

INSERT INTO employee
VALUES ('Rafferty', 31),
       ('Jones', 33),
       ('Heisenberg', 33),
       ('Robinson', 34),
       ('Smith', 34),
       ('Williams', NULL);
</syntaxhighlight>