我想知道如何使用连接将此SQL重写为单个选择。我有一个很长的方式，如下所示基本上得到“项目开始里程碑”的最小日期和“生产上线”里程碑的最大日期。
一些背景是sql用于项目管理应用程序，它根据发布基线里程碑集跟踪项目里程碑。我需要一个proc，它接受一个项目ID的CSV列表，并让它选择项目启动里程碑的最小startDate（StatusCode.cid = 37）和最大生产上线里程碑（StatusCode.cid = 77）
这是我现在正在使用的虚拟SQL：
CREATE PROC rpt_rainbow
@ProjectIDs NVARCHAR(1000)
AS
DECLARE @MinBRSProjectStartDate DATETIME
DECLARE @MinBRSReleaseStartDate DATETIME
DECLARE @MaxProdProjectEndDate DATETIME
DECLARE @MaxProdReleaseEndDate DATETIME
SELECT @MinBRSProjectStartDate = MIN (pm.startDate)
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID AND pm.ProjectID IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
WHERE sc.cid =37
SELECT @MinBRSReleaseStartDate = MIN(rel.startDate)
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID AND rel.milestonecid IN (37)
WHERE ProjectId IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
SELECT @MaxProdProjectEndDate = MAX (pm.endDate)
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID AND pm.ProjectID IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
WHERE sc.cid =77
SELECT @MaxProdReleaseEndDate = MAX(rel.endDate)
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID AND rel.milestonecid IN (77)
WHERE ProjectId IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
select isnull(@MinBRSProjectStartDate, @MinBRSReleaseStartDate) as MinBRS_StartDate,
isnull(@MaxProdProjectEndDate, @MaxProdReleaseEndDate) as MaxProd_EndDate
这是我的分割功能：
CREATE FUNCTION dbo.Split
( @Delimiter varchar(5),
@List varchar(8000)
)
RETURNS @TableOfValues table
( RowID smallint IDENTITY(1,1),
[Value] varchar(50)
)
AS
BEGIN
DECLARE @LenString int
WHILE len( @List ) > 0
BEGIN
SELECT @LenString =
(CASE charindex( @Delimiter, @List )
WHEN 0 THEN len( @List )
ELSE ( charindex( @Delimiter, @List ) -1 )
END
)
INSERT INTO @TableOfValues
SELECT substring( @List, 1, @LenString )
SELECT @List =
(CASE ( len( @List ) - @LenString )
WHEN 0 THEN ''
ELSE right( @List, len( @List ) - @LenString - 1 )
END
)
END
RETURN
END
以下是所涉及表格的定义：
CREATE TABLE [dbo].[ProjectMilestone](
[ProjectMilestoneId] [int] NOT NULL,
[ProjectId] [int] NOT NULL,
[MilestoneCID] [int] NOT NULL,
[StartDate] [datetime] NOT NULL,
[EndDate] [datetime] NOT NULL,
[RAGStatusCID] [int] NOT NULL,
[CompletionStatusCID] [int] NOT NULL,
[StatusText] [nvarchar](max) NOT NULL,
[ReportingPriority] [int] NULL,
[Owner] [nvarchar](50) NOT NULL,
[Added] [datetime] NOT NULL,
[LastUpdate] [datetime] NOT NULL,
[UpdateBy] [nvarchar](50) NOT NULL,
CONSTRAINT [PK_ProjectMilestone] PRIMARY KEY CLUSTERED
(
[ProjectMilestoneId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[ProjectMilestone] WITH CHECK ADD CONSTRAINT [FK_ProjectMilestone_Project] FOREIGN KEY([ProjectId])
REFERENCES [dbo].[Project] ([ProjectId])
GO
ALTER TABLE [dbo].[ProjectMilestone] CHECK CONSTRAINT [FK_ProjectMilestone_Project]
-----------------------------------------------------------------------------------------------
CREATE TABLE [dbo].[Project](
[ProjectId] [int] NOT NULL,
[ProjectName] [nvarchar](255) NOT NULL,
[ProjectRegistration] [nvarchar](50) NOT NULL,
[CaseManagerBenId] [nvarchar](50) NOT NULL,
[ClarityId] [nvarchar](50) NOT NULL,
[ParentProjectId] [int] NULL,
[ReleaseId] [int] NOT NULL,
[CompletionStatusCID] [int] NOT NULL,
[ProjectTypeCID] [int] NOT NULL,
[Budget] [money] NOT NULL,
[BusinessObjective] [nvarchar](max) NOT NULL,
[Benefit] [nvarchar](max) NOT NULL,
[Added] [datetime] NOT NULL,
[LastUpdate] [datetime] NOT NULL,
[UpdateBy] [nvarchar](50) NOT NULL,
[StakeholderList] [nvarchar](1000) NULL,
CONSTRAINT [PK_Project] PRIMARY KEY CLUSTERED
(
[ProjectId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[Project] WITH CHECK ADD CONSTRAINT [FK_Project_Project] FOREIGN KEY([ParentProjectId])
REFERENCES [dbo].[Project] ([ProjectId])
GO
ALTER TABLE [dbo].[Project] CHECK CONSTRAINT [FK_Project_Project]
GO
ALTER TABLE [dbo].[Project] WITH CHECK ADD CONSTRAINT [FK_Project_Release] FOREIGN KEY([ReleaseId])
REFERENCES [dbo].[Release] ([ReleaseId])
GO
ALTER TABLE [dbo].[Project] CHECK CONSTRAINT [FK_Project_Release]
--------------------------------------------------------------------------------------------
CREATE TABLE [dbo].[StatusCode](
[CID] [int] NOT NULL,
[CodeName] [nvarchar](50) NOT NULL,
[Description] [nvarchar](max) NOT NULL,
[SCID] [int] NOT NULL,
[ReportingPriority] [int] NULL,
CONSTRAINT [PK_StatusCode] PRIMARY KEY CLUSTERED
(
[CID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
--------------------------------------------------------------------------------------------
CREATE TABLE [dbo].[ReleaseSchedule](
[ReleaseScheduleID] [int] NOT NULL,
[ReleaseID] [int] NOT NULL,
[MilestoneCID] [int] NOT NULL,
[StartDate] [datetime] NOT NULL,
[EndDate] [datetime] NOT NULL,
[Added] [datetime] NOT NULL,
[LastUpdate] [datetime] NOT NULL,
[UpdateBy] [nvarchar](50) NOT NULL,
CONSTRAINT [PK_ReleaseSchedule] PRIMARY KEY CLUSTERED
(
[ReleaseScheduleID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[ReleaseSchedule] WITH CHECK ADD CONSTRAINT [FK_ReleaseSchedule_Release] FOREIGN KEY([ReleaseID])
REFERENCES [dbo].[Release] ([ReleaseId])
GO
ALTER TABLE [dbo].[ReleaseSchedule] CHECK CONSTRAINT [FK_ReleaseSchedule_Release]
答案 0 :(得分：3)
有两点需要注意，第一点是你可以将4个查询减少到2个
SELECT
@MinBRSProjectStartDate = MIN (CASE WHEN sc.cid=37 then pm.startDate END),
@MaxProdProjectEndDate = MAX (CASE WHEN sc.cid=77 then pm.endDate END)
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID
AND pm.ProjectID IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
WHERE sc.cid in (37,77)
SELECT
@MinBRSReleaseStartDate = MIN(CASE WHEN rel.milestonecid=37 then rel.startDate end),
@MaxProdReleaseEndDate = MAX(CASE WHEN rel.milestonecid=77 then rel.endDate end)
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID AND rel.milestonecid IN (37,77)
WHERE ProjectId IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
这两组之间真的没有办法加入，所以没有必要尝试。但是你可以CROSS JOIN两个单行结果来获得一个选择中的所有4列：
SELECT ISNULL(A,C) as MinBRS_StartDate, ISNULL(B,D) AS MaxProd_EndDate
FROM
(
SELECT
MIN (CASE WHEN sc.cid=37 then pm.startDate END) A,
MAX (CASE WHEN sc.cid=77 then pm.endDate END) B
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID
AND pm.ProjectID IN (SELECT value FROM fn_Split(@ProjectIDs, ','))
WHERE sc.cid in (37,77)
) X,
(
SELECT
MIN(CASE WHEN rel.milestonecid=37 then rel.startDate end) C,
MAX(CASE WHEN rel.milestonecid=77 then rel.endDate end) D
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID AND rel.milestonecid IN (37,77)
WHERE ProjectId IN (SELECT value FROM fn_Split(@ProjectIDs, ','))) Y
但是因为你在2对中使用ISNULL，所以最好保留4个有针对性的索引选择并且只是对它们进行子查询。由于您使用SPLIT值4次，因此将其缓存在临时表中是有意义的。 ISNULL应该足够聪明，一旦第一个选择返回值，就不需要评估第二个选择。
declare @ids table (id int)
insert @ids SELECT distinct value FROM fn_Split(',', @ProjectIDs) V
SELECT
ISNULL(
(SELECT MIN (pm.startDate)
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID
INNER JOIN @ids I ON pm.ProjectID = I.ID
WHERE sc.cid =37),
(SELECT MIN(rel.startDate)
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID
INNER JOIN @ids I ON p.ProjectID = I.ID
WHERE rel.milestonecid IN (37))) AS MinBRS_StartDate,
ISNULL(
(SELECT MAX (pm.endDate)
FROM StatusCode sc
INNER JOIN ProjectMilestone pm ON sc.CID = pm.MilestoneCID
INNER JOIN @ids I ON pm.ProjectID = I.ID
WHERE sc.cid =77),
(SELECT MAX(rel.endDate)
FROM Project p
INNER JOIN ReleaseSchedule rel ON rel.ReleaseID = p.ReleaseID
INNER JOIN @ids I ON p.ProjectID = I.ID
WHERE rel.milestonecid IN (77))) AS MaxProd_EndDate