Query with switch function requests parameter value [duplicate] - excel

Question

This question already has answers here:
Why does this query require a parameter?
(2 answers)
Closed 3 years ago.
Background: Excel worksheet as front end to an Access database. Excel contains VBA code and uses ADODB to move values into and out of the tables in Access.
One column is a composite value which describes a complex priority relationship. One digit for priority level (1-6), one letter for more granular level (A-C), and a type of project (Safety, Security, Enviro, etc.) The values look like "2B - Maint.", "2A - ProcCntl"
I need to sort the results of a select * query in different ways. Sometimes with the typical Alpha sort which would list 1A values before 1B before 4C. Other times I need to sort all the Safety as a group, Maint. as another, etc. A simple alpha sort on the project type doesn't work because the manager wants a specific order.
I am using the Switch function to assign the order. I have found a couple of ways to make this work in Access but they all ask for a parameter value when I run the query. Entering a blank value gets the desired result. Moving the query into the VBA of Excel returns an error complaining of an empty parameter.
Here is one of the "working" queries:
SELECT *, Mid([Priority],6,2) AS ProjClass,
Switch(ProjClass="Sa",1,ProjClass="En",2,ProjClass="Se",3,ProjClass="6S",4,ProjClass="Qu",5,ProjClass="Pr",6,ProjClass="Ma",7,ProjClass="Bu",8)
AS [FirstSort]
FROM tblProjects
ORDER BY [FirstSort] ASC, [Priority] ASC;
When I run this through the VBA I get
Run-time error "No value given for one or more required parameters."
When I run it in Access a "Enter Parameter Value" dialog opens asking for FirstSort. I click through and see the result is correctly sorted.
The root question: Why is Access seeing FirstSort as a parameter and not a field name?
I think I need to understand that before I can fix the VBA issue.

Answer 1

More research has revealed yet another Access quirk: The problem is that MS Access does not allow AS clauses in the ORDER BY clause.
So a little experimentation lead me to change the ORDER BY clause to ORDER BY 3 ASC, [Priority] ASC;
I chose the three because it is the third field expression in the query. It works but it would be great if someone could clarify the specific rule that makes it work.
Hat tip: Why does this query require a parameter? and onedaywhen's answer.

Answer 2

ProjClass is a field created during execution of the query. Before that when the SQL engine is determining an execution plan for the query it will not recognize that field name so assumes it is parameter. SORT is done at the end of the query and by that time the engine knows which is the third field.
An alternative is to create another table called something like tblPriority with 2 columns ProjectClass and SortOrder
ProjClass SortOrder
Sa 1
En 2
Se 3
6S 4
Qu 5
Pr 6
Ma 7
Bu 8
and use a JOIN
SELECT A.* FROM tblProjects AS A
LEFT JOIN tblPriority as B
ON B.ProjClass = Mid(A.Priority,6,2)
ORDER BY SortOrder