Question

Is the following problematic?

DELETE a
FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData a
WHERE EXISTS
        (
        SELECT * 
        FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData b
        WHERE 
            b.[Past28Days] = 1 AND
            a.[Index] = b.[Index]
        HAVING SUM(b.Amount) = 0
        )

Reason I’m slightly uneasy about using the above script is that if I run the following it errors:

SELECT * 
FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData b
WHERE 
    b.[Past28Days] = 1
HAVING SUM(b.Amount) = 0

I understand why this script errors => the select is not grouped on anything therefore the processor does not like the aggregation in the HAVING clause.

But as a sub-query this error does not occur – why? Is this a problematic approach?

EDIT

Ended up using the following:

DELETE a
FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData a
WHERE a.[Index] IN
    (
    SELECT [Index] 
    FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData
    WHERE [Past28Days] = 1
    GROUP BY [Index] 
    HAVING SUM(Amount) = 0
    )

But as suggested in answer the following is more readable by simply adding the GROUP BY into the sub-query:

DELETE a
FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData a
WHERE EXISTS
    (
    SELECT * 
    FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData b
    WHERE 
            b.[Past28Days] = 1 AND
            a.[Index] = b.[Index]
    GROUP BY b.[Index]
    HAVING SUM(b.Amount) = 0
    )

Answer 1

It is legal to omit group by and still perform aggregations, therefore having is still a way of limiting results:

select sum(x)
from
(
  select 1 x union all select 2
) a
having sum(x) = 3

Exists() work because everything in select list is ignored. Exists() looks for rows only, and terminates as soon as one is found. You might add group by b.Index to make intent clear to anyone reviewing the code later, or rewrite it using inner join and derived table.

DELETE a
FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData a
INNER JOIN
        (
        SELECT b.[Index]
        FROM WHAnalysis.dbo.tb_r12027dxi_CalculatedData b
        WHERE 
            b.[Past28Days] = 1
        GROUP BY b.[Index]
        HAVING SUM(b.Amount) = 0
        ) b1
   ON a.[Index] = b1.[Index]