SQL - Returning all rows even if count is zero for item

Question

I am performing a count based on a date range. Currently the query does return the correct result but I require additional information. In it's current form, the query shows the item with the correct count. However I need all items to be shown, even if their count is zero for the date range specified.

Here is the SQL code:

INSERT INTO @CreationCount (BaselineID, Name)

SELECT distinct [BaselineID],[Name] 
FROM [Baseline_INFO] 

DECLARE @ReqType TABLE (Type nvarchar(128))
INSERT INTO @ReqType (Type)
SELECT DISTINCT Tree.Type as 'Requirement Type'
FROM [TREE]
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN [Baseline_INFO] ON [Baseline_INFO].[BaselineID]=[Tree].[Baseline_ID]
WHERE [Project_INFO].[Name] = 'Address Book' AND [Baseline_INFO].[Name] = 'Current
Baseline' 
Group By Tree.Type

SELECT Tree.Type as 'Requirement Type', COUNT(Tree.Type) as 'Number in Creation Range' 
FROM [Tree] 
INNER JOIN @ReqType As RT on RT.Type = Tree.Type
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN @CreationCount AS CCount ON CCount.BaselineID=Tree.Baseline_ID 
WHERE [Project_INFO].[Name] = 'Address Book' AND CCount.Name = 'Current Baseline' 
AND [Tree].[creationDate] >= ('2010-01-01') and [Tree].[creationDate] < ('2020-01-01') 
GROUP BY tree.Type

When I execute this query I get the following result:

https://dl.dropbox.com/u/17234826/SQLresult.png

This result is correct however I need all requirement types to be list, even if there are no requirements in the creation range, i.e.

https://dl.dropbox.com/u/17234826/SQLresult1.png

I have tried using various joins, IFNULL and ISNULL but I haven't got anything to work.

If someone could point me in the right direction I'd appreciate it.

Answer 1

Modify the second query

SELECT Tree.Type as 'Requirement Type',
       COUNT(CASE WHEN [Tree].[creationDate] >= ('2010-01-01') and [Tree].[creationDate] < ('2020-01-01') THEN Tree.Type END) AS 'Number in Creation Range'
FROM [Tree] 
INNER JOIN @ReqType As RT on RT.Type = Tree.Type
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN @CreationCount AS CCount ON CCount.BaselineID=Tree.Baseline_ID 
WHERE [Project_INFO].[Name] = 'Address Book' AND CCount.Name = 'Current Baseline' 
GROUP BY tree.Type

Answer 2

Generally speaking, to get records with counts of 0, you need an outer join of some sort so you count the rows that have no match. You can even use a cross-join of all the options you want counts for. Alternatively, I often implement this type of count by using a correlated subquery. Here are a couple of general examples:

-- Get count using left join
select c.customer_id,
    count(o.order_id) as num
from customers c
    left join orders o on c.customer_id = o.customer_id
group by c.customer_id

-- Get count using correlated subquery
select c.customer_id,
    (select count(*) from orders where customer_id = c.customer_id) as Num
from customers c

Another possibility, if you've got a working query, is to hack together something like this:

-- Create a cte of the original query that we will use multiple times
;WITH cte as (
    SELECT Tree.Type as 'Requirement Type'
        , COUNT(Tree.Type) as 'Number in Creation Range' 
    FROM [Tree] 
        INNER JOIN @ReqType As RT on RT.Type = Tree.Type
        INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
        INNER JOIN @CreationCount AS CCount ON CCount.BaselineID=Tree.Baseline_ID 
    WHERE [Project_INFO].[Name] = 'Address Book' AND CCount.Name = 'Current Baseline' 
        AND [Tree].[creationDate] >= ('2010-01-01') and [Tree].[creationDate] < ('2020-01-01') 
    GROUP BY tree.Type
)
-- Grab the counts of records with matches
select *
from cte
-- Grab the zero counts (records not in the original query)
union all
select Tree.Type, 0
from [Tree]
where Tree.Type not in (
    select Tree.Type
    from cte
)