分析：
由于优化器无法判断或获得远端表的统计信息，故原执行计划默认会采取把远程表（无论大小）拉到本地再连接的方式执行，
这样如果远程表较大的情况将会比较缓慢，像上述查询耗时在1分钟以上。
原SQL语句：
Select
Wb.*,
(Select Wi.Nextarrivedate
From Mbs7_Oms.Xs_Warearriveinfo@Dc.Moonbasadb.Com Wi
Where Wi.Warecode = Wb.Warecode) As Nextarrivedate
From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wb ---这里远端表较大
Inner Join (Select Wa.Stylecode, Max(Wa.Warecode) As Warecode
From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wa
Inner Join (Select Stylecode
From Dc_Support.Kh_Visitpage Vis
Where Vis.Cuscode = :B1
And Vis.Addtime >= Trunc(Sysdate - 31)
And Vis.Addtime < Trunc(Sysdate - 30)
And Rownum <= 5
Order By Addtime Desc) Vis
On Wa.Stylecode = Vis.Stylecode
Group By Wa.Stylecode) Wc
On Wb.Warecode = Wc.Warecode
解决方案：
用以下HINTS方式加上去后，优化器会调整执行计划，把运算端控制在WB,并且远端表MBS7_CRM.WI_WAREBASE表字段的索引(STYLECODE)缺少连接索引，于是在目标端创建以下索引进行优化，优化后COST从7百多下降到20，运行2秒内可返回结果，性能增加不少。
远端表创建索引：
create index mbs7_crm.ix_WI_WAREBASE_STYLECODE on mbs7_crm.WI_WAREBASE(STYLECODE)调优后的SQL：
Select
Wb.*,
(Select Wi.Nextarrivedate
From Mbs7_Oms.Xs_Warearriveinfo@Dc.Moonbasadb.Com Wi
Where Wi.Warecode = Wb.Warecode) As Nextarrivedate
From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wb ---远端表较大
Inner Join (Select Wa.Stylecode, Max(Wa.Warecode) As Warecode
From Mbs7_Crm.Wi_Warebase@Dc.Moonbasadb.Com Wa
Inner Join (Select Stylecode
From Dc_Support.Kh_Visitpage Vis
Where Vis.Cuscode = :B1
And Vis.Addtime >= Trunc(Sysdate - 31)
And Vis.Addtime < Trunc(Sysdate - 30)
And Rownum <= 5
Order By Addtime Desc) Vis
On Wa.Stylecode = Vis.Stylecode
Group By Wa.Stylecode) Wc
On Wb.Warecode = Wc.Warecode©版权声明：本文为 天凯DBS 的原创文章，转载请附上原文出处链接及本声明，否则将追究法律责任。
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