优化查询。FOR XML PATH 或一些替代方案？

Question

有什么办法可以优化FOR XML PATH语句吗？或者也许我应该使用另一种方法？

目前的方法根本不可接受。这需要几分钟。我知道视图是一个非常大的联盟，需要时间来消耗它，但也许是另一种方式......

这是查询：

SELECT t.serialNumber as TVM
  ,[issuanceDate] as transactionDate
  ,ioy.tvmTransactionId as TVM_TRANS_ID
  ,STUFF((SELECT ', ' + stv.carrierSN
    FROM HERMES.wts.v_SaleTransactionView as stv
    WHERE stv.tvmTransactionId = ioy.tvmTransactionId
    and stv.serialNumber = 'M040'
    FOR XML PATH ('')), 1, 2, '') as [serial_numbers]
  FROM [hermes].[wts].[IOYLog] ioy
  left join Hermes.hermes.Terminals t on ioy.tp_terminalId = t.tp_terminalId
  left join hermes.hermes.POS p on t.tp_POSId = p.tp_POSId
  left join [Hermes].[wts].[IOUPaymentStatus] [is] on [is].[tp_paymentStatusId] = ioy.status
  WHERE [is].includeInReports = 1 
  and (issuanceDate BETWEEN '2017/09/01' AND '2017/09/08') and (t.serialNumber = 'M040')
  ORDER BY transactionDate

执行计划：https : //www.brentozar.com/pastetheplan/?id=Sk7i98Wjb

Answer 1

在Sentry One Plan Explorer 中查看这一点，有四个主要的索引问题，所有这些问题都与隐藏一个昂贵的残差谓词的索引扫描有关：

以下四个索引将消除这些扫描并加速此执行计划：

--- Currently scanning 7 million rows to return 11
CREATE INDEX give_me_a_name
ON [wts].[Prepaid_TransactionLog]
    ([tvmTransactionId])
INCLUDE
    (tp_terminalId, tp_POSId, status);

-- Currently scanning 21.5 million rows to return zero    
CREATE INDEX give_me_a_name
ON [wts].[KBETicketTransactionLog]
    ([tvmTransactionId])
INCLUDE
    (carrierSN, tp_terminalId, tp_POSId, status);

-- Currently scanning 6.25 million rows to return 12
CREATE INDEX give_me_a_name
ON [wts].[Intercity_TicketTransactionLog]
    ([tvmTransactionId])
INCLUDE
    (formType, status, tp_terminalId, tp_POSId);

第四个索引稍微复杂一些，因为键涉及integer到 match的转换[wts].[IOYLog].[tvmTransactionId]。这意味着要么改变现有列，要么提供一个计算列，如下所示：

-- New computed column, should be instant to add (metadata only)
ALTER TABLE [mazovian].[Transaction]
ADD [SequenceAsInteger] AS CONVERT(integer, [Sequence])

-- Currently scanning 61.6 million rows to return 70
CREATE INDEX give_me_a_name
ON [mazovian].[Transaction]
    ([SequenceAsInteger])
INCLUDE
    (Id, Sequence, Terminal_id, Detail_id, Location_id);

添加这四个索引应该会显着加快查询速度。与所有索引更改一样，您应该在决定部署之前在测试系统上对其进行评估。

您可以考虑许多其他小的索引改进来避免计划中的关键查找：

• 添加[status]到现有索引[IOYLog].[IX_IOYLog_tp_terminalId_tvmTransactionId_issuanceDate_owedAmount]
• 添加carrierSN, tp_POSId, 和status到索引[TransportTransactionLog].[IX_TransportTransactionLog_tp_terminalId_tvmTransaction_KK]
• 添加End_Status到索引[Transaction_Distribution].[I_mazovian_Transaction_Distribution_Ticket_id]