Question

我有一个查询，当稍微修改时会将其运行时间从大约37秒减少到4秒。连接或返回的列没有变化。

慢速查询（37秒）：

declare @PeriodFrom DateTime
declare @PeriodTo DateTime
Set @PeriodFrom = '2012-06-01'
Set @PeriodTo = '2012-06-30'

Select
  0 as PrimaryAccount,
  0 as PrintOrder,
  Cast(Null as integer) as ID,
  Sum(IsNull(MT.Amount, 0)) as Amount,
  Cast(0 as Money) as NetAmount,
  Cast(0 As Money) as TaxAmount,
  Cast(0 as Money) as AmountOutstanding,
  Cast(0 as Money) as AmountPaid,
  'Balance brought forward' as Description
From
  db_site4.dbo.AccountReceivable P
Join
  db_site4.dbo.ARType ART on ART.ARTypeID = P.ARTypeID and ART.ARTypeID = 24
left Join
  db_site4.dbo.vw_MemberTransactions MT
on
  P.AccountReceivableID = MT.AccountReceivableID
where 
  (MT.AccountingDate <= @PeriodFrom or MT.AccountingDate is null)
and
  (Authorised = 1 or Authorised is Null)
and
  IsHidden = 0
and
  P.MemberID = 123

以上的SQL I / O统计信息：

Table 'Payment'. Scan count 16, logical reads 23558, physical reads 19, read-ahead reads 5448.
Table 'InvoiceItemPayment'. Scan count 4, logical reads 22237, physical reads 51, read-ahead reads 13432.
Table 'UnallocatedPayment'. Scan count 12, logical reads 431, physical reads 1, read-ahead reads 80.
Table 'AccountReceivable'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0.
Table 'ARType'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0.
Table 'Invoice'. Scan count 11116, logical reads 116984, physical reads 190, read-ahead reads 30910.
Table 'InvoiceItem'. Scan count 5122, logical reads 99786, physical reads 316, read-ahead reads 46236.

现在查询在4秒内返回：

declare @PeriodFrom DateTime
declare @PeriodTo DateTime
Set @PeriodFrom = '2012-06-01'
Set @PeriodTo = '2012-06-30'

Select
  0 as PrimaryAccount,
  0 as PrintOrder,
  Cast(Null as integer) as ID,
  Sum(IsNull(MT.Amount, 0)) as Amount,
  Cast(0 as Money) as NetAmount,
  Cast(0 As Money) as TaxAmount,
  Cast(0 as Money) as AmountOutstanding,
  Cast(0 as Money) as AmountPaid,
  'Balance brought forward' as Description
From
  db_site4.dbo.AccountReceivable P
Join
  db_site4.dbo.ARType ART on ART.ARTypeID = P.ARTypeID and ART.ARTypeID = 24
left Join
  db_site4.dbo.vw_MemberTransactions MT
on
  P.AccountReceivableID = MT.AccountReceivableID
where 
  (MT.AccountingDate <= @PeriodFrom or MT.AccountingDate is null)
and
  (Authorised = 1 or Authorised is Null)
and
  (IsHidden = 0 or IsHidden is null)
and
  P.MemberID = 123

以上的SQL I / O统计信息：

Table 'Payment'. Scan count 6271, logical reads 19857, physical reads 0, read-ahead reads 0.
Table 'UnallocatedPayment'. Scan count 2, logical reads 4, physical reads 0, read-ahead reads 0.
Table 'InvoiceItemPayment'. Scan count 4399, logical reads 33400, physical reads 0, read-ahead reads 0.
Table 'InvoiceItem'. Scan count 10581, logical reads 60682, physical reads 4, read-ahead reads 0.
Table 'Invoice'. Scan count 3, logical reads 22102, physical reads 3, read-ahead reads 0.
Table 'AccountReceivable'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0.
Table 'ARType'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0.

我的问题是：如果唯一的更改是将IsHidden = 0替换为(IsHidden = 0 or IsHidden IS NULL)，那么两者之间的执行时间会有怎样的差异？（从底部开始3行）

Answer 1

取决于您在IsHidden中的数据和索引。

如果你有很多空值和良好的索引，可能是执行计划首先在'IsHidden = 0'之前取得它们，所以它的工作速度比仅扫描'IsHidden = 0'要快。

Answer 2

当您添加附加子句以包含ISNULL时，您可能会从AccountRecievable返回更多行。反过来，您将在视图中加入更多行。这意味着必须从视图的基表中读取更多行，从而增加查询时间。

这里的逻辑来自查看您提供的IO统计数据。对于您提供的查询“不可见”的表有其他读取。考虑在视图的基表上查看索引策略。

SQL Server查询响应时间变化很大，代码更改很少

2 个答案: