Access SQL - I need a query to count fields based on several criteria

Question

I have used stackoverflow for years and usually I have been able to find what I need through searching but I apologize, I couldn't find an example like this. I am extremely new to this stuff but love doing it at work to assist with various projects.

I work in the insurance claims industry, we have insurance claims as electronic files. The supervisors do reviews of these files, simply called a file review. I have an Access db which I use to track all the file reviews at work.

Sometimes as Claims Supervisors we are doing a file review on our OWN associates, meaning the associate reports to me. Other times I am doing a file review on an associate who reports to a DIFFERENT supervisor.

My master table looks like this (with lots of other columns) and each record indicates a file review:

ClaimNumber | Supervisor | Reviewer
----------- | -----------| ------------
1---------- | ---Bob-----| Bob 
2---------- | ---Bob-----| Amy 
3---------- | ---John----| Amy 
4---------- | ---John----| Dean
5---------- | ---John----| John 
6---------- | ---Dean----| Dean 
7---------- | ---Dean----| Dean 
8---------- | ---Dean----| Bob 
9---------- | ---Kyle----| Bob
10--------- | ---Bob-----| Shawn 

Depending on if a join is used, please note that sometimes a supervisor name is not listed a single time in the reviewer column. Likewise, sometimes a reviewer name is not listed a single time in the supervisor column.

So, I need a single query that returns

Reviewer  ------  TotalReviews ----  Self_Reviews ---- Cross_Reviews

The reviewer is all the unique reviewers

TotalReviews is a count of how many times that reviewer's name is listed in reviewer column

Self reviews is a count of how many times that reviewer's name is listed in the reviewer column where their name is equal to the supervisor name for that particular record

Cross reviews is a count of how many times that reviewer's name is listed in the reviewer column where their name is NOT equal to the supervisor name for that particular record

Bob has 3 reviews total, 1 self, 2 cross

Amy has 2 reviews total, 0 self, 2 cross

Dean has 3 reviews total, 2 self, 1 cross

John has 1 review, 1 self, 0 cross

Shawn has 1 review, 0 self, 1 cross

I know this seems complex to me but I am hoping someone can assist to make it much easier. I am just using Access so any oracle or other SQL syntax may not work.

Answer 1

There is a simple trick you can use here: summing over indicator functions.

The indicator function for self reviews would be Switch(Supervisor = Reviewer,1,True,0) .

That leads to the following query:

SELECT 
  T.Reviewer, 
  COUNT(*) AS TotalReviews, 
  SUM(Switch(T.Supervisor = T.Reviewer,1,True,0)) AS Self_Reviews,
  SUM(Switch(T.Supervisor <> T.Reviewer,1,True,0)) AS Cross_Reviews 
FROM TableName T
GROUP BY T.Reviewer

In other environments than Access, the indicator function would typically be the fllowing:

CASE WHEN Supervisor = Reviewer THEN 1 ELSE 0 END