等效查询，不同的结果和执行时间

Question

编辑：查询计划链接到：

Bad Query

Good Query

所以我正在研究一个 MSSQL 系统，并且我正在重写一些查询。我决定主要通过将谓词从 WHERE 子句中移出并将它们填充到我的 JOIN 子句中来使用我的谓词。当我这样做时，它返回的行数是原来的两倍，执行时间从几秒到几分钟。

我想知道发生了什么，因为我认为查询分析器通常会将谓词填充到 JOIN 子句中，因为这些行最终会被丢弃。

任何关于为什么这些查询不等价的帮助将不胜感激，我只是不够强大，不知道在哪里看..

好查询：

FROM [CONNECT_PROD].[dbo].[CRM_C005] c005 
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_FI] fi ON c005.ID_FI = fi.ID
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_CPPE] kp ON c005.ID_PE = kp.ID_PE AND  fi.id = kp.id_fi
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] vko ON c005.F7010 = vko.code 
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_VF] vf on vf.id_fi = fi.id and vf.VerkOrg = vko.code
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] land ON fi.land = land.code 
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] title ON kp.Titel = title.code and title.loskz = 0 and title.KatSperre = 0 and title.sprachenr = 0 and title.katnr = 23
WHERE kp.loskz = 0
and vko.loskz = 0
and vko.KatSperre = 0
and vko.sprachenr = 0
and vko.katnr = 274
and vko.ExtKey = '0014'
and land.loskz = 0
and land.KatSperre = 0
and land.sprachenr = 1000
and land.katnr = 2
and fi.loskz = 0
and fi.F7029 = 0
and vf.loskz = 0
and vf.F7023 = 0
and vf.F7152 = 0
and c005.del = 0
and kp.f7017 = 0

错误查询：

FROM [CONNECT_PROD].[dbo].[CRM_C005] c005 
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_FI] fi ON c005.ID_FI = fi.ID AND fi.loskz = 0 AND fi.F7029 = 0
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_CPPE] kp ON c005.ID_PE = kp.ID_PE AND fi.id = kp.id_fi AND kp.loskz = 0 AND kp.f7017 = 0
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] vko ON c005.F7010 = vko.code AND vko.loskz = 0 AND vko.KatSperre = 0 AND vko.sprachenr = 0 AND vko.katnr = 274 and vko.ExtKey = '0014'
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_VF] vf on vf.id_fi = fi.id and vf.VerkOrg = vko.code AND vf.loskz = 0 AND vf.F7023 = 0 AND vf.F7152 = 0
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] land ON fi.land = land.code AND land.loskz = 0 AND land.KatSperre = 0 AND land.sprachenr = 1000 AND land.katnr = 2
LEFT JOIN [CONNECT_PROD].[dbo].[CRM_KA] title ON kp.Titel = title.code and title.loskz = 0 and title.KatSperre = 0 and title.sprachenr = 0 and title.katnr = 23
WHERE c005.del = 0

Answer 1

假设这个例子：我有一个包含 100,000 个电话的表格。有某些类型的电话：呼入和呼出。当我写一个查询是

SELECT * 
FROM calls c
LEFT JOIN calltypes ct
ON c.calltypeID = ct.calltypeID
WHERE c.calltypeID = 1 --Assume this is inbound

此查询将仅返回我的呼叫表中的入站呼叫。

现在，如果我写：

SELECT * 
    FROM calls c
    LEFT JOIN calltypes ct
    ON c.calltypeID = ct.calltypeID
    AND c.calltypeID = 1 

我将返回 100,000 行。左连接找不到合适的连接条件，所以对 ct 表的值返回空值。这是一个示例，说明当您在连接条件中使用 where 子句时，您的查询可能会返回更多的行。

Answer 2

通过在您将其变为常规连接的位置引用连接的外侧
你也可以这样做

FROM [CONNECT_PROD].[dbo].[CRM_C005] c005 
JOIN [CONNECT_PROD].[dbo].[CRM_FI] fi 
       ON fi.ID    = c005.ID_FI 
      and            c005.del = 0
      and fi.loskz = 0
      and fi.F7029 = 0
JOIN [CONNECT_PROD].[dbo].[CRM_CPPE] kp 
       ON kp.ID_PE = c005.ID_PE  
      AND kp.id_fi = c005.ID_FI 
      and kp.loskz = 0 
      and kp.f7017 = 0
JOIN [CONNECT_PROD].[dbo].[CRM_KA] vko 
       ON vko.code      = c005.F7010     
      and vko.loskz     = 0
      and vko.KatSperre = 0
      and vko.sprachenr = 0
      and vko.katnr     = 274
      and vko.ExtKey    = '0014'
JOIN [CONNECT_PROD].[dbo].[CRM_VF] vf 
       on vf.id_fi   = c005.ID_FI 
      and vf.VerkOrg = vko.code 
      and vf.loskz   = 0
      and vf.F7023   = 0
      and vf.F7152   = 0
JOIN [CONNECT_PROD].[dbo].[CRM_KA] land 
       ON land.code      = fi.land  
      and land.loskz     = 0
      and land.KatSperre = 0
      and land.sprachenr = 1000
      and land.katnr     = 2
JOIN [CONNECT_PROD].[dbo].[CRM_KA] title 
       ON title.code      = kp.Titel 
      and title.loskz     = 0 
      and title.KatSperre = 0 
      and title.sprachenr = 0 
      and title.katnr     = 23