如何使用 MIN MAX 函数优化 SQL 查询

Question

这是我的查询

SELECT
    [Car].CarId AS Id,
    CAST(MIN(ISNULL([Dates].StartDate, [Reco].InsStartDate)) AS date) AS StartDate,
    CAST(MAX(ISNULL([Dates].EndDate, [Reco].InsEndDate)) AS date) AS EndDate
FROM
    dbo.TabReco [Reco]
    INNER JOIN dbo.Insurance [INS] ON [INS].InsId = [Reco].InsId
    INNER JOIN dbo.InsuranceCar [Details] ON [Details].INSCarId = [INS].INSCarId
    INNER JOIN dbo.CarHistory [Car] ON [Car].CarHistId = [Details].CarHistId
    INNER JOIN dbo.InsuranceRiskDates [Dates] ON [Dates].INSId = [INS].INSId
GROUP BY
    [Reco].Number,
    [Car].CarId

当我运行这个查询时，它需要很长时间。问题在于日期的 MIN/MAX 部分。

CAST(MIN(ISNULL([Dates].StartDate, [Reco].InsStartDate)) AS date) AS StartDate,
CAST(MAX(ISNULL([Dates].EndDate, [Reco].InsEndDate)) AS date) AS EndDate

如果我删除该部分，那么查询会更快。有没有办法优化这样的查询？或者这是不可能的。

Answer 1

看起来你在使用 INNER JOIN 时不需要 ISNULL。

别管那个了，把那部分去掉就行了。

除非您在 [Dates].StartDate 和 [Dates].EndDate 上允许 null 或者如果您使用 LEFT JOIN ：

SELECT
    [Car].CarId AS Id,
    CAST(MIN(ISNULL([Dates].StartDate, [Reco].InsStartDate)) AS date) AS StartDate,
    CAST(MAX(ISNULL([Dates].EndDate, [Reco].InsEndDate)) AS date) AS EndDate
FROM
    dbo.TabReco [Reco]
    INNER JOIN dbo.Insurance [INS] ON [INS].InsId = [Reco].InsId
    INNER JOIN dbo.InsuranceCar [Details] ON [Details].INSCarId = [INS].INSCarId
    INNER JOIN dbo.CarHistory [Car] ON [Car].CarHistId = [Details].CarHistId
    LEFT JOIN dbo.InsuranceRiskDates [Dates] ON [Dates].INSId = [INS].INSId
GROUP BY
    [Reco].Number,
    [Car].CarId

您可能需要为连接区域中不是主键的每一列建立索引。

已编辑：除了索引之外，我还有一个想法，试试这个：

SELECT Id,
CAST(MIN(StartDate) AS date) AS StartDate,
CAST(MIN(EndDate) AS date) AS EndDate
FROM
( 
    SELECT [Reco].Number,
    [Car].CarId AS Id,
    [Dates].StartDate, [Dates].EndDate
    FROM
    dbo.TabReco [Reco]
    INNER JOIN dbo.Insurance [INS] ON [INS].InsId = [Reco].InsId
    INNER JOIN dbo.InsuranceCar [Details] ON [Details].INSCarId = [INS].INSCarId
    INNER JOIN dbo.CarHistory [Car] ON [Car].CarHistId = [Details].CarHistId
    INNER JOIN dbo.InsuranceRiskDates [Dates] ON [Dates].INSId = [INS].INSId
    WHERE [Dates].StartDate IS NOT NULL

    UNION ALL

    SELECT [Reco].Number,
    [Car].CarId AS Id,
    [Reco].InsStartDate AS StartDate, 
    [Reco].InsEndDate AS EndDate
    FROM
    dbo.TabReco [Reco]
    INNER JOIN dbo.Insurance [INS] ON [INS].InsId = [Reco].InsId
    INNER JOIN dbo.InsuranceCar [Details] ON [Details].INSCarId = [INS].INSCarId
    INNER JOIN dbo.CarHistory [Car] ON [Car].CarHistId = [Details].CarHistId
    LEFT JOIN dbo.InsuranceRiskDates [Dates] ON [Dates].INSId = [INS].INSId
    WHERE [Dates].StartDate IS NULL
) x
GROUP BY Number, Id