Multiple Counts in SQL Query

Question

Give the following simple table structure:

Departments
PK - DeptID    DeptName
--------------------------
1              Department 1
2              Department 2
3              Department 3
4              Department 4

Groups
PK - GroupdID    DeptID
--------------------------
1                1
2                1
3                3 
4                4
5                2
6                3
7                1
8                3

Inventory
PK - ItemID    GroupID
--------------------------
1              2
2              3
3              8
4              1
5              4
6              5
7              1
8              2
9              2
10             3
11             7

Is there a way without using subqueries (which is easy) where I could get a listing of the departments, the count of the groups in each department, and the count of the inventory in each department?

Example Output:

DeptID    DeptName          GroupCount      ItemCount
-----------------------------------------------------
1         Department 1      3               6
2         Department 2      1               1
3         Department 1      3               3
4         Department 4      1               1

My gut is telling me it's just a simple matter of getting the GROUP BY statements correct, but so far I'm drawing a blank. If it does require the use of subqueries, this isn't a problem. I just wanted to confirm for future reference.

NOTE: Using SQL Server 2000 for this particular problem

Answer 1

What quassnoi said.

Answer 2

Sorry I am not sitting in front of my SQL Server. Here is a first attempt for you. I might not understand you desired result correctly but maybe you can use this as a starting point?

SELECT 
  Department.DeptId,
  Department.DeptName,
  Group.GroupId,
  COUNT (Inventory.GroupId) as TotalItems
FROM
  Department
  INNER JOIN Groups
    On (Department.DeptId = Groups.DeptId)
  INNER JOIN Inventory
    On (Inventory.GroupId = Groups.GroupId)
GROUP BY
  Department.DeptId,
  Department.DeptName
  Group.GroupId,
  Inventory.GroupId

Answer 3

Following is at least one way to get the results.

SELECT d.DeptID, d.DeptName, ISNULL(g.Groups, 0), ISNULL(t.TotalItems, 0)
FROM 
  Departments d
  LEFT OUTER JOIN (
    SELECT d.DeptID, Groups = COUNT(*)
    FROM Departments d
         INNER JOIN Groups g ON g.DeptID = d.DeptID
    GROUP BY d.DeptID
  ) g ON g.DeptID = d.DeptID
  LEFT OUTER JOIN (
    SELECT d.DeptID, TotalItems = COUNT(*)
    FROM Departments d
         INNER JOIN Groups g ON g.DeptID = d.DeptID
         INNER JOIN Inventory i ON i.GroupID = g.GroupID
    GROUP BY d.DeptID
  ) t ON t.DeptID = d.DeptID

Answer 4

SELECT  d.deptID,
        COUNT(DISTINCT g.GroupID) AS Groups,
        COUNT(DISTINCT i.ItemID) AS Items
FROM    Departments d
LEFT JOIN 
        Groups g
ON      g.deptID = d.deptID
LEFT JOIN
        Items i
ON      i.GroupID = g.GroupID
GROUP BY
        d.deptID

The results produced are:

deptID  Groups  Items
-----   ------  -----
1       3       6 
2       1       1
3       3       3
4       1       1

This will also produce correct 0's for the Departments that have no Groups, or having only Groups without Items.

Answer 5

Here's my try...

declare @Depatments table
(
DeptID  int
,DeptName  varchar(15)
)

declare @Groups table
(
GroupID  int
,DeptID  int
)

declare @Inventory table
(
ItemID    int
,GroupID  int
)

INSERT INTO @Depatments VALUES (1,'Department 1')
INSERT INTO @Depatments VALUES (2,'Department 2')
INSERT INTO @Depatments VALUES (3,'Department 3')
INSERT INTO @Depatments VALUES (4,'Department 4')

INSERT INTO @Groups VALUES (1,1)
INSERT INTO @Groups VALUES (2,1)
INSERT INTO @Groups VALUES (3,3)
INSERT INTO @Groups VALUES (4,4)
INSERT INTO @Groups VALUES (5,2)
INSERT INTO @Groups VALUES (6,3)
INSERT INTO @Groups VALUES (7,1)
INSERT INTO @Groups VALUES (8,3)

INSERT INTO @Inventory VALUES (1 ,2)
INSERT INTO @Inventory VALUES (2 ,3)
INSERT INTO @Inventory VALUES (3 ,8)
INSERT INTO @Inventory VALUES (4 ,1)
INSERT INTO @Inventory VALUES (5 ,4)
INSERT INTO @Inventory VALUES (6 ,5)
INSERT INTO @Inventory VALUES (7 ,1)
INSERT INTO @Inventory VALUES (8 ,2)
INSERT INTO @Inventory VALUES (9 ,2)
INSERT INTO @Inventory VALUES (10,3)
INSERT INTO @Inventory VALUES (11,7)


--works with derived tables
SELECT
    d.DeptName,dt_g.CountOf AS GroupCount, dt_i.CountOf AS InventotyCount
    FROM @Depatments  d
        LEFT OUTER JOIN (SELECT
                             COUNT(*) AS CountOf,DeptID
                             FROM @Groups
                             GROUP BY DeptID
                        ) dt_g ON d.DeptID=dt_g.DeptID
        LEFT OUTER JOIN (SELECT
                             COUNT(*) AS CountOf,g.DeptID
                             FROM @Groups               g
                                 INNER JOIN @Inventory  i ON g.GroupID=i.GroupID
                             GROUP BY DeptID
                        ) dt_i ON d.DeptID=dt_i.DeptID