添加条件查询会使时间增加超过2400%

更新:我会尽快得到查询计划.

我们的查询效果不佳,需要4分钟才能完成特定组织.在通常的重新编译之后,存储的proc和更新统计信息没有帮助,我们将if Exists(...)重写为select count(*)...以及4分钟到70毫秒的存储过程.条件使得70毫秒查询需要4分钟的问题是什么？查看示例

这些都需要4分钟以上:

if (
  SELECT COUNT(*)       
    FROM ObservationOrganism  omo
    JOIN Observation          om  ON  om.ObservationID  = omo.ObservationMicID
    JOIN Organism             o   ON  o.OrganismID      = omo.OrganismID
    JOIN ObservationMicDrug   omd ON  omd.ObservationOrganismID = omo.ObservationOrganismID
    JOIN SIRN                 srn ON  srn.SIRNID        = omd.SIRNID
    JOIN OrganismDrug         od  ON  od.OrganismDrugID = omd.OrganismDrugID
  WHERE
    om.StatusCode IN ('F', 'C')
    AND o.OrganismGroupID <> -1
    AND od.OrganismDrugGroupID <> -1
    AND (om.LabType <> 'screen' OR om.LabType IS NULL)) > 0

print 'records';       

-

IF (EXISTS(
  SELECT *       
    FROM ObservationOrganism  omo
    JOIN Observation          om  ON  om.ObservationID  = omo.ObservationMicID
    JOIN Organism             o   ON  o.OrganismID      = omo.OrganismID
    JOIN ObservationMicDrug   omd ON  omd.ObservationOrganismID = omo.ObservationOrganismID
    JOIN SIRN                 srn ON  srn.SIRNID        = omd.SIRNID
    JOIN OrganismDrug         od  ON  od.OrganismDrugID = omd.OrganismDrugID
  WHERE
    om.StatusCode IN ('F', 'C')
    AND o.OrganismGroupID <> -1
    AND od.OrganismDrugGroupID <> -1
    AND (om.LabType <> 'screen' OR om.LabType IS NULL))

print 'records'

这一切都需要70毫秒:

Declare @recordCount INT;
SELECT @recordCount = COUNT(*)       
    FROM ObservationOrganism  omo
    JOIN Observation          om  ON  om.ObservationID  = omo.ObservationMicID
    JOIN Organism             o   ON  o.OrganismID      = omo.OrganismID
    JOIN ObservationMicDrug   omd ON  omd.ObservationOrganismID = omo.ObservationOrganismID
    JOIN SIRN                 srn ON  srn.SIRNID        = omd.SIRNID
    JOIN OrganismDrug         od  ON  od.OrganismDrugID = omd.OrganismDrugID
  WHERE
    om.StatusCode IN ('F', 'C')
    AND o.OrganismGroupID <> -1
    AND od.OrganismDrugGroupID <> -1
    AND (om.LabType <> 'screen' OR om.LabType IS NULL);

IF(@recordCount > 0)
  print 'records';

对我来说,为什么将完全相同的Count(*)查询移动到if语句会导致这种降级或者为什么'Exists'慢于Count.我甚至尝试过exists()a select CASE WHEN Exists(),它仍然是4分钟以上.