How do I count rows with two properties in one index scan in SQL?

Question

I have a table Units where I have rows ItemId, ItemCreationDate, ItemUnitsCount. ItemId is a primary key and I have a clustered index over it.

I need to output the following: for each day I need to count separately

1. items that were created in that day and have zero ItemUnitsCount
2. items that were created in that day and have nonzero ItemUnitsCount

and output the count and the date and on any day there can be any number of item of both kinds, maybe none. Each kind of items should be reported separately, so for any day I can have no rows, one row or two rows.

So I crafted the following query:

(SELECT ItemCreationDate, COUNT(ItemId) AS ComputedCount, 1 AS CountType
 FROM Items WHERE ItemUnitsCount<>0 GROUP BY ItemCreationDate )
UNION ALL
(SELECT ItemCreationDate, COUNT(ItemId) AS ComputedCount, 2 AS CountType
 FROM Items WHERE ItemUnitsCount=0 GROUP BY ItemCreationDate )

and this works okay, but when I looks at the actual execution plan I see two clustered index scans one of which has predicate ItemUnitsCount=0 and another has predicate ItemUnitsCount<>0.

ItemUnitsCount can be changed several times over lifetime of the table row, so I'd rather not build an index for it.

Is there a way to build a query with the same effect that results in one index scan instead of two?

• Philᵀᴹ: Is it ok to output the result in 1 row? If so, it's easy
• sharptooth: @Phil: Nope, that should be separate rows.
• Nick Chammas: You have this question tagged for both 2008 R2 and Azure. Is that correct? (Not that it matters for the question, just for categorization.)
• sharptooth: @Nick Chammas: I heard that SQL Azure is a modified version of SQL Server 2k8 R2. Not sure though.
• Nick Chammas: Yes, it's the "cloud" version of SQL Server, hosted and managed by Microsoft with major administration differences and some important feature differences.

Answer 1

Group by your condition

SELECT
 ItemCreationDate,
 COUNT(ItemId) AS ComputedCount,
 CASE WHEN ItemUnitsCount = 0 THEN 2 ELSE 1 END AS CountType
FROM
 Items
GROUP BY
 ItemCreationDate,
 CASE WHEN ItemUnitsCount = 0 THEN 2 ELSE 1 END;

• Nick Chammas: This is the simplest, most direct solution to the OP's problem.

Answer 2

SELECT
 ItemCreationDate
 , SUM(CASE WHEN ItemUnitsCount <> 0 THEN 1 ELSE 0 END) AS CountType1
 , SUM(CASE WHEN ItemUnitsCount = 0 THEN 1 ELSE 0 END) AS CountType2
FROM
 dbo.Items
GROUP BY
 ItemCreationDate

• JNK: He wants them on separate rows I think...
• Nick Chammas: @JNK A PIVOT should do the trick.