Select rows in one table, based on column values in another table? - sql

Question

I need to select one column for each matching row in another table. Sounds simple, but there's a twist.
I have one table that has Company IDs, and defines Companies.
I have another table that defines Departments in those companies.
I have a third table that contains the various Department StatusCodes.
The code that I have below works just fine, and is exactly what I want it to do. But I have to hardcode into the query which departments to look for. I'd like it to sub-select based on department codes it finds in the Departments table, and not require me to hard code each possible department that might exist at that company.
I need to select the matching department status from DepartmentStatus based upon what Departments exist for a company as defined in DepartmentsStatus table.
I suspect it's a pivot table, but they are a bit above my level.
(Company Table)
Company_ID Company_Name
-------------------------
1 Home Office
2 Stanton Office
3 NYC Office
(Departments Table)
CompanyID Department_Code
----------------------------
1 Sales
1 Inventory
1 Retail
1 Maint
2 OtherDept
2 ThatDept
2 BobsDept
(DepartmentStatus Table)
Company_ID Department StatusCode
-----------------------------------------
1 Sales InReview
1 Inventory InReview
1 Retail Ready
1 Maint Done
2 OtherDept InReview
2 ThatDept Research
2 BobsDept InReview
Note: I use "TOP 1", even though there is a unique index on Company_ID+Department, so there will never be more than one matching row.
So, for Company_ID=1:
select Company_ID,
(select top 1 StatusCode from DepartmentStatus ds where ds.Company_ID = cm.Company_ID and ds.Department='Sales') as SalesStatus
(select top 1 StatusCode from DepartmentStatus ds where ds.Company_ID = cm.Company_ID and ds.Department='Inventory') as InvStatus
(select top 1 StatusCode from DepartmentStatus ds where ds.Company_ID = cm.Company_ID and ds.Department='Retail') as RetailStatus
(select top 1 StatusCode from DepartmentStatus ds where ds.Company_ID = cm.Company_ID and ds.Department='Main') as MaintStatus
from Company cm
Where cm.CompanyID=1
Results:
Company_ID SalesStatus InvStatus RetailStatus MaintStatus
--------------- --------------- ---------- ------------- ------------
1 InReview InReview Ready Done
Or, for CompanyID=2:
select Company_ID,
(select top 1 StatusCode from DepartmentStatus ds where ds.CompanyID = cm.Company_ID and ds.Department='OtherDept') as OtherDeptStatus
(select top 1 StatusCode from DepartmentStatus ds where ds.CompanyID = cm.Company_ID and ds.Department='ThatDept') as ThatDeptStatus
(select top 1 StatusCode from DepartmentStatus ds where ds.CompanyID = cm.Company_ID and ds.Department='BobsDept') as BobsDeptStatus
from Company cm
Where cm.CompanyID=2
Results:
Company_ID OtherDeptStatus ThatDeptStatus BobsDeptStatus
---------- ---------------- -------------- --------------
2 InReview Research InReview
Thus, For Company 1, I need to go get the status for Departments Sales, Inventory, Retail, and Maint.
But for Company 2, I need to get the status for Departments OtherDept, ThatDept, and BobsDept.
The steps that I think describe what I am trying to do is:
Get list of Departments for Company 1 from Departments Table.
For each of these Departments in Step 1, query DepartmentStatus table for Department equals that department.
For Company 1, query get StatusCode for Departments "Sales, Inventory, Retail, and Maint"
For Company 2, query get StatusCode for Departments "OtherDept, thatDept, and BobsDept."
etc etc
The problem is, I do not know ahead of time (at query time) which departments exist for each Company, so I need to sub-select based upon what departments actually exist for each company.
There are a few other S.O. answers already that are close what I'm asking for, suggesting the use of a JOIN to accomplish this, however, they all assume that you know the values you want to query ahead of time when writing the join statement.
I'm looking for a solution to this problem, not just a correction on my current attempt. If you have a better idea entirely on how to accomplish this, I'd love to see it.

Answer 1

You seem to be looking for conditional aggregation. Using this technique, your query can be simplified as follows, to avoid the need for multiple inline subqueries:
select Company_ID,
max(case when ds.Department='Sales' then ds.StatusCode end) as SalesStatus,
max(case when ds.Department='Inventory' then ds.StatusCode end) as InvStatus,
max(case when ds.Department='Retail' then ds.StatusCode end) as RetailStatus,
max(case when ds.Department='Main' then ds.StatusCode end) as MaintStatus
from
Company cm
inner join DepartmentStatus ds on ds.Company_ID = cm.Company_ID
Where cm.CompanyID=1
group by cm.CompanyID

Answer 2

this would be my (untested) caveman way of solving your problem.
the only thing you need to know in advance is how many different departments you have in the company with the most departments.
DROP TABLE IF EXISTS Iddepartmentstatus;
DECLARE #Result TABLE(
Companyid INT,
Department1 NVARCHAR(MAX),
Department2 NVARCHAR(MAX),
Department3 NVARCHAR(MAX),
Department4 NVARCHAR(MAX),
Department5 NVARCHAR(MAX));
CREATE TABLE Iddepartmentstatus(
Num INT IDENTITY(1, 1),
Department NVARCHAR(MAX),
Statuscode NVARCHAR(MAX));
DECLARE #IDCompany TABLE(
Num INT IDENTITY(1, 1),
Companyid INT,
Companyname NVARCHAR(MAX));
INSERT INTO #IDCompany (Companyid,
Companyname)
SELECT Company_Id,
Company_Name
FROM Company;
DECLARE #Departmentcount INT = 0,
#Departmentstatuscount INT = 0,
#Companycount INT = 0;
WHILE #Companycount <=
(
SELECT MAX(Num)
FROM #IDCompany)
BEGIN
INSERT INTO Iddepartmentstatus (Department,
Statuscode)
SELECT Department,
Statuscode
FROM Departmentstatus
WHERE Company_Id = #Companycount;
INSERT INTO #Result (Companyid)
SELECT #Companycount AS T;
INSERT INTO #Result (Department1)
SELECT IIF(1 <=
(
SELECT MAX(Num)
FROM #IDCompany), Department + ': ' + Departmentstatus, NULL)
FROM Iddepartmentstatus
WHERE Num = 1;
INSERT INTO #Result (Department2)
SELECT IIF(2 <=
(
SELECT MAX(Num)
FROM #IDCompany), Department + ': ' + Departmentstatus, NULL)
FROM Iddepartmentstatus
WHERE Num = 2;
INSERT INTO #Result (Department3)
SELECT IIF(3 <=
(
SELECT MAX(Num)
FROM #IDCompany), Department + ': ' + Departmentstatus, NULL)
FROM Iddepartmentstatus
WHERE Num = 3;
INSERT INTO #Result (Department4)
SELECT IIF(4 <=
(
SELECT MAX(Num)
FROM #IDCompany), Department + ': ' + Departmentstatus, NULL)
FROM Iddepartmentstatus
WHERE Num = 4;
INSERT INTO #Result (Department5)
SELECT IIF(5 <=
(
SELECT MAX(Num)
FROM #IDCompany), Department + ': ' + Departmentstatus, NULL)
FROM Iddepartmentstatus
WHERE Num = 5;
TRUNCATE TABLE Iddepartmentstatus;
SET #Companycount = #Companycount + 1;
END;
DROP TABLE IF EXISTS Iddepartmentstatus;