T-SQL Self Join in combination with aggregate function

Question

Hi,

i have the following table.

CREATE TABLE [dbo].[Tree](
 [AutoID] [int] IDENTITY(1,1) NOT NULL,
 [Category] [varchar](10) NULL,
 [Condition] [varchar](10) NULL,
 [Description] [varchar](50) NULL,
 CONSTRAINT [PK_Tree] PRIMARY KEY CLUSTERED 
(
 [AutoID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

the data looks like this:

INSERT INTO [Test].[dbo].[Tree]
           ([Category]
           ,[Condition]
           ,[Description])
     VALUES ('1','Alpha','Type 1')
INSERT INTO [Test].[dbo].[Tree]
           ([Category]
           ,[Condition]
           ,[Description])
     VALUES ('1','Alpha','Type 1')
INSERT INTO [Test].[dbo].[Tree]
           ([Category]
           ,[Condition]
           ,[Description])
     VALUES ('2','Alpha','Type 2')
INSERT INTO [Test].[dbo].[Tree]
           ([Category]
           ,[Condition]
           ,[Description])
     VALUES ('2','Alpha','Type 2')

go

I try now to do the following:

SELECT Category,COUNT(*) as CategoryCount FROM Tree where Condition = 'Alpha' group by Category

but i wish also to get the Description for each Element. I tried several subqueries, self joins etc. i always come to the problem that the subquery cannot return more than one record.

The problem is caused by a poor database design which i cannot change and i run out of ideas to get this done in a single query ;-(

Answer 1

If you need description, you have to include it in the aggregate

SELECT  Category ,
        [Description] ,
        COUNT(*) AS CategoryCount
FROM    Tree
WHERE   Condition = 'Alpha'
GROUP BY Category ,
        [Description]