How to get a single record in a one to many relation based on the value of this record - sql

Question

I have two tables, one contains a list of projects, another contains requests for this project. I would like to get the project number and the requests record. The status can be: Red, Yellow, Green, Open
How can I make sure that the 1 status record being shown follows the logic that when there is a Red one, show the red one, when there is no red one but there is a yellow one show this yellow one so on...
;WITH
numberTest as(
SELECT dbo.ServiceRequest.ID as numId,
ROW_NUMBER() OVER (PARTITION BY dbo.ServiceRequest.Project_ID order by Project_ID) AS RN1
FROM dbo.ServiceRequest
),
CTEVrequest AS
(
SELECT dbo.ServiceRequest.ID, dbo.ServiceRequest.Project_ID
FROM dbo.ServiceRequest
LEFT JOIN numberTest ON numberTest.numId = dbo.ServiceRequest.ID
WHERE numberTest.RN1 = 1
AND
dbo.ServiceRequest.ID = CASE
WHEN EXISTS(
select srvReq.ID
from dbo.ServiceRequest as srvReq
where requestStatus.ServiceStatus = 'R' AND srvReq.Project_ID = dbo.ServiceRequest.Project_ID)
THEN (select srvReq.ID
from dbo.ServiceRequest as srvReq
where requestStatus.ServiceStatus = 'R' AND srvReq.Project_ID = dbo.ServiceRequest.Project_ID)
WHEN EXISTS(
select srvReq.ID
from dbo.ServiceRequest as srvReq
where requestStatus.ServiceStatus = 'Y' AND srvReq.Project_ID = dbo.ServiceRequest.Project_ID)
THEN (select srvReq.ID
from dbo.ServiceRequest as srvReq
where requestStatus.ServiceStatus = 'Y' AND srvReq.Project_ID = dbo.ServiceRequest.Project_ID)
END)
SELECT DISTINCT
dbo.Project.ProjectNumber,
dbo.Project.ID,
CTEVrequest.ServiceReqStatus,
CTEVrequest.ServiceStatus
FROM dbo.Project
LEFT JOIN CTEVrequest ON CTEVrequest.Project_ID = dbo.Project.ID
LEFT JOIN dbo.Project ON dbo.ServiceRequest.Project_ID = dbo.Project.ID
The problem is I get the "Subquery returned more than 1 value" error and I have no clue how to make the result check if there exists a record with Red and if not select the one with Yellow and so on.

Answer 1

Probably I did not understand you right, but looks like your query is supposed to do this:
SELECT *
FROM dbo.Project p
OUTER APPLY
(
SELECT TOP 1 sr.*
FROM dbo.ServiceRequest sr
WHERE sr.Project_ID = p.Project_ID
/* AND sr.ServiceStatus in ('R', 'Y') */
ORDER BY
CASE
WHEN sr.ServiceStatus = 'R' THEN 1
WHEN sr.ServiceStatus = 'Y' THEN 2
ELSE 3
END
) sr

Answer 2

Why don't you create a table that functions as a key for the statuses? For example:
IF OBJECT_ID('tempdb..#LevelKey') IS NOT NULL
DROP TABLE #LevelKey;
CREATE TABLE #LevelKey
(LevelText [varchar](255),
LevelValue INT);
INSERT INTO #LevelKey VALUES
('Red',1),
('Orange',2),
('Yellow',3),
('Green',4);
Now, join the project level to this key. When you want to grab the highest rank, you could do something like:
SELECT TOP 1 *
FROM Table
INNER JOIN #LevelKey ON LevelText = Whatever
ORDER BY LevelValue ASC
But that only works for one. So I'm not even sure why I included that. To bring back a group, you're going to have to do something like this:
SELECT ProjectID, MAX(LevelValue) AS LevelValue
FROM Table
INNER JOIN #LevelKey ON LevelText = Whatever
GROUP BY ProjectID