Question

need some your help with a query.

I have a table Managers (ManagerId, ManagerName)

I have a table Statuses (StatusId, StatusName)
(There’s about 10 statuses in that table)

I have a table Clients (ClientId, ClientName, ManagerId, StatusId, WhenAdded)
(WhenAdded is a datetime type)

It’s obvious that field 'ManagerId' refers to a table 'Managers' and field 'StatusId' refers to a table 'Statuses'.

User wants to get some statistics about Managers over a period of time (from startDate to endDate using field 'WhenAdded') in the following table.

Columns:

ManagerName, NumberOfClients, NumberOfClientsWithStatus1, NumberOfClientsWithStatus2, NumberOfClientsWithStatus3 and so on.

Number of columns with name NumberOfClientsWithStatusI where i is a number of statuses equal to number of rows in table 'Statuses'.

How can I do that?

t-sql, sql server 2008 r2 express edition.

Answer 1

SELECT
    ManagerName,
    COUNT(*) AS NumberOfClients,
    COUNT(CASE WHEN S.StatusId = 1 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus1,
    COUNT(CASE WHEN S.StatusId = 2 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus2,
    COUNT(CASE WHEN S.StatusId = 3 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus3,
    ...
FROM
   Clients C
   JOIN
   Managers M ON C.ManagerId = M.ManagerId
   JOIN
   Statuses S ON C.StatusId = S.StatusId
WHERE
    M.WhenAdded BETWEEN @startDate AND @endDate
GROUP BY
    M.ManagerName

Note: there is no clean way to add arbritrary numbers of status columns in SQL (not just SQL Server) because its a fixed column output. You’d have to change the query for status, unless you deal with this in the client

Edit, after comment

SELECT
    ManagerName,
    COUNT(*) AS NumberOfClients,
    COUNT(CASE WHEN S.StatusId = 1 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus1,
    COUNT(CASE WHEN S.StatusId = 2 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus2,
    COUNT(CASE WHEN S.StatusId = 3 THEN 1 ELSE NULL END) AS NumberOfClientsWithStatus3,
    ...
FROM
   Managers M ON C.ManagerId = M.ManagerId
   LEFT JOIN
   Clients C
   LEFT JOIN
   Statuses S ON C.StatusId = S.StatusId
WHERE
    M.WhenAdded BETWEEN @startDate AND @endDate
GROUP BY
    M.ManagerName