Sql 统计select语句中匹配的项

我们有一个针对一些相当大的表执行的存储过程，当连接到一个较大的表时，它也会记录有多少记录与相应的批处理id相匹配。我试图弄清楚的是，我是否可以使用计数函数或其他方法来改进这一点？正在尝试摆脱嵌套的SELECT COUNT（*）语句。CCTransactions表有140万行，BatchItems表有660万行

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

---

当DBMS支持窗口聚合函数时，可以将其重写为

COUNT(*) OVER (PARTITION BY Batch_ID)

当然，这只返回SELECT返回的每个批次ID的行数。如果内部联接导致行数减少，则该行数不正确

然后将标量子查询重写为联接可能更有效（取决于您的DBMS）：

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

我对计数（*）进行了多次测试，虽然它确实减少了集合统计IO上的扫描计数，但增加了计划的子树成本。现在让我测试子查询的内部联接，看看它是如何执行的。