Question

如何为下表设置唯一键约束，以确保Date / BeginTime和Date / EndTime之间的日期/时间跨度不与其他记录重叠？如果我需要添加一个计算列，那么数据类型和计算是什么？

Column Name   Data Type
Date          date
BeginTime     time(7)
EndTime       time(7)

感谢。

Answer 1

我不相信你可以在SQL Server中使用UNIQUE约束来做到这一点。 Postgres具有此功能，但要在SQL Server中实现它，您必须使用触发器。由于您的问题是“如何使用唯一键约束来执行此操作”，因此正确的答案是“您不能”。如果您曾问过“我如何强制执行此非重叠约束”，那么就有答案。

Answer 2

Alexander Kuznetsov展示了一种可行的方式。 Storing intervals of time with no overlaps

参见Joe Celko的文章：Contiguous Time Periods

这是表格和第一个间隔：

CREATE TABLE dbo.IntegerSettings(SettingID INT NOT NULL,
  IntValue INT NOT NULL,
  StartedAt DATETIME NOT NULL,
  FinishedAt DATETIME NOT NULL,
  PreviousFinishedAt DATETIME NULL,

  CONSTRAINT PK_IntegerSettings_SettingID_FinishedAt 
      PRIMARY KEY(SettingID, FinishedAt),

  CONSTRAINT UNQ_IntegerSettings_SettingID_PreviousFinishedAt
      UNIQUE(SettingID, PreviousFinishedAt),

  CONSTRAINT FK_IntegerSettings_SettingID_PreviousFinishedAt
    FOREIGN KEY(SettingID, PreviousFinishedAt)
    REFERENCES dbo.IntegerSettings(SettingID, FinishedAt),

  CONSTRAINT CHK_IntegerSettings_PreviousFinishedAt_NotAfter_StartedAt
      CHECK(PreviousFinishedAt <= StartedAt),

  CONSTRAINT CHK_IntegerSettings_StartedAt_Before_FinishedAt 
      CHECK(StartedAt < FinishedAt)
);

INSERT INTO dbo.IntegerSettings
    (SettingID, IntValue, StartedAt, FinishedAt, PreviousFinishedAt)
VALUES(1, 1, '20070101', '20070103', NULL);

约束强制执行这些规则：

设置
下一个窗口必须在上一个窗口结束后开始
两个不同的窗口不能引用与前一个窗口相同的窗口

Answer 3

-- this is a unique key that allows for null in EndTime field
--  This Unique Index could be clusteres optionally instead of the traditional primary key being clustered 
CREATE UNIQUE NONCLUSTERED INDEX  
[UNQ_IDX_Date_BeginTm_EndTm_UniqueIndex_With_Null_EndTime] ON [MyTableName]
(
    [Date] ASC,
    [BeginTime] ASC,
    [EndTime] ASC
) 

GO


-- this is a traditional PK Constraint that is clustered but EndTime is
--- Not Null
-- it is possible that this table would not have a traditional Primary Key
ALTER TABLE dbo.MyTable ADD CONSTRAINT
    PK_Date_BeginTm_EndTm_EndTimeIsNotNull PRIMARY KEY CLUSTERED 
    (
    Date,
    BeginTime,
    EndTime
    ) 

GO

-- HINT - Control your BeginTime and EndTime secconds and milliseconds at 
-- all insert and read points 
-- you want 13:01:42.000  and 13:01:42.333  to evaluate and compare the
-- exact way you expect from a KEY perspective

SQL Server唯一键约束日期/时间跨度

3 个答案: