Question

我有一个我正在尝试优化的SQL查询。

有没有更好的方法可以避免在这里使用子查询？得到了关于使用Row_number（）的建议，发布此内容并进行一些更正

DECLARE @curdate DATETIME
SET @curdate = GETDATE()

SELECT DISTINCT 
    SIS.StudentID, StudentCoverage.StudentCoverageDataID, 
    Student.FirstName, Student.LastName, 
    Student.DateOfBirth, Student.Gender,
    ASMT.AssessmentDate
FROM 
    SIS (NOLOCK)
INNER JOIN 
    SISMaster (NOLOCK) ON SISMaster.SISID = SIS.SISID
INNER JOIN 
    Assessment ASMT ON SIS.StudentID = ASMT.StudentId 
INNER JOIN 
    StudentCoverage (NOLOCK) ON StudentCoverage.StudentID = SIS.StudentID
INNER JOIN 
    Organization (NOLOCK) ON StudentCoverage.OrgID = Organization.OrganizationID
INNER JOIN 
    Student (NOLOCK) ON Student.StudentID = SIS.StudentID
INNER JOIN 
    StudentCoverageData (NOLOCK) ON StudentCoverageData.StudentCoverageID = StudentCoverage.StudentCoverageID
           AND StudentCoverageData.StudentCoverageDataID = (SELECT TOP 1 StudentCoverageData.StudentCoverageDataID
                                                            FROM StudentCoverage 
                                                            INNER JOIN StudentCoverageData ON StudentCoverageData.StudentCoverageID = StudentCoverage.StudentCoverageID
                                                            WHERE StudentCoverage.StudentId = SIS.StudentID
                                                              AND StudentCoverageData.Active = 1 
                                                              AND StudentCoverageData.EffectiveDate <= @curdate 
                                                              AND (StudentCoverageData.ExitDate IS NULL OR StudentCoverageData.ExitDate > @curdate)
                                                           ORDER BY StudentCoverageData.AsOfDate DESC)

Answer 1

子查询中的所有表都存在于内连接子句中，因此您可以像这样重写查询：

;WITH temps AS
(
    DECLARE @curdate DATETIME = GETDATE()

    SELECT  
        SIS.StudentID, StudentCoverage.StudentCoverageDataID, 
        Student.FirstName, Student.LastName, 
        Student.DateOfBirth, Student.Gender,
        ASMT.AssessmentDate,
        ROW_NUMBER() OVER (PARTITION BY StudentCoverageData.StudentCoverageDataID ORDER BY StudentCoverageData.AsOfDate) AS RowIndex
    FROM 
        SIS (NOLOCK)
    INNER JOIN 
        SISMaster (NOLOCK) ON SISMaster.SISID = SIS.SISID
    INNER JOIN 
        StudentCoverage (NOLOCK) ON StudentCoverage.StudentID = SIS.StudentID
    INNER JOIN 
        Organization (NOLOCK) ON StudentCoverage.OrgID = Organization.OrganizationID
    INNER JOIN 
        Student (NOLOCK) ON Student.StudentID = SIS.StudentID
    INNER JOIN 
        StudentCoverageData (NOLOCK) ON StudentCoverageData.StudentCoverageID = StudentCoverage.StudentCoverageID          
    WHERE StudentCoverageData.Active = 1
    AND StudentCoverageData.EffectiveDate <= @curdate
    AND (StudentCoverageData.ExitDate IS NULL OR StudentCoverageData.ExitDate > @curdate)
)
SELECT  * FROM temps t
WHERE t.RowIndex = 1

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1 个答案: