Question

My table IncomingLetter has a foreign key to a table Department, which has an ID and a column Short_Name.

I’m using this query to count the incoming letters assigned to a department.

SELECT COUNT(DocumentNumber) AS TotalNumberIncomingLetters
FROM IncomingLetter
WHERE Assigned_To_Department=1;

Whereas this works I want to make a query based upon the short name and not based upon the ID.

SELECT COUNT(DocumentNumber) AS TotalNumberIncomingLetters
FROM IncomingLetter
WHERE Assigned_To_Department.Short_Name="My Department Name";

This does not work, whereas I found examples that are using this syntax. However, it is probably important to notice, that I m using this query in MS access.

Answer 1

You should use

SELECT COUNT(il.DocumentNumber) AS TotalNumberIncomingLetters
FROM IncomingLetter il
 INNER JOIN Department d on d.ID = il.Assigned_To_Department
WHERE d.Short_Name="My Department Name";

The “My Department Name” text is actually stored in the Departments table, and only the number (1) is stored in the IncomingLetter table, in the field Assigned_To_Department.
Asking for Assigned_To_Department.Short_Name basically asks the number 1 to get it’s Short_Name field, that does not make sense.

You need to tell the database engine two things in these scenarios:

• which tables are connected – IncomingLetter and Departments in this case (the inner join part)
• how they are connected – by setting their Assigned_To_Department and ID fields respecively (the on ... part