counting items that match within select statement - sql

Question

We have a stored procedure that executes against some fairly large tables and while joining to a larger table it is also keeping a tally of how many records match the corresponding batch_id. What I am trying to figure out is can I improve this with a function for the count or some other means? Trying to get rid of the nested SELECT COUNT(*) statement. The CCTransactions table is 1.4 million rows and the BatchItems is 6.6 million rows.
SELECT a.ItemAuthID, a.FeeAuthID, a.Batch_ID, a.ItemAuthCode,
a.FeeAuthCode, b.Amount, b.Fee,
(SELECT COUNT(*) FROM BatchItems WHERE Batch_ID = a.Batch_ID) AS BatchCount,
ItemBillDate, FeeBillDate, b.AccountNumber,
b.Itemcode, ItemAuthToken, FeeAuthToken,
cc.ItemMerchant, cc.FeeMerchant
FROM CCTransactions a WITH(NOLOCK)
INNER JOIN BatchItems b WITH(NOLOCK)
ON a.Batch_ID = b.Batch_ID
INNER JOIN CCConfig cc WITH(NOLOCK)
ON a.ClientCode = cc.ClientCode
WHERE ((ItemAuthCode > '' AND ItemBillDate IS NULL)
OR (FeeAuthCode > '' AND FeeBillDate IS NULL))
AND TransactionDate BETWEEN DATEADD(d,-7,GETDATE())
AND convert(char(20),getdate(),101) + ' ' + #Cutoff
ORDER BY TransactionDate

Answer 1

When your DBMS supports WIndowed Aggregate Functions you can rewrite it to
COUNT(*) OVER (PARTITION BY Batch_ID)
Of course this only returns the number of rows per Batch_ID returned by the SELECT. if the inner join results in less rows, it's not the correct number.
Then it might be more efficient (depending on your DBMS) to rewrite the Scalar Subquery to a join:
SELECT a.ItemAuthID, a.FeeAuthID, a.Batch_ID, a.ItemAuthCode,
a.FeeAuthCode, b.Amount, b.Fee,
dt.BatchCount,
ItemBillDate, FeeBillDate, b.AccountNumber,
b.Itemcode, ItemAuthToken, FeeAuthToken,
cc.ItemMerchant, cc.FeeMerchant
FROM CCTransactions a WITH(NOLOCK)
INNER JOIN BatchItems b WITH(NOLOCK)
ON a.Batch_ID = b.Batch_ID
INNER JOIN CCConfig cc WITH(NOLOCK)
ON a.ClientCode = cc.ClientCode
INNER JOIN
(
SELECT BatchCount, COUNT(*) AS BatchCount
FROM BatchItems
GROUP BY Batch_ID
) AS dt ON a.Batch_ID = dt.Batch_ID
WHERE ((ItemAuthCode > '' AND ItemBillDate IS NULL)
OR (FeeAuthCode > '' AND FeeBillDate IS NULL))
AND TransactionDate BETWEEN DATEADD(d,-7,GETDATE())
AND convert(CHAR(20),getdate(),101) + ' ' + #Cutoff
ORDER BY TransactionDate