如何有效地选择小于和大于给定值的最近值？

Question

我有两个表,一个用于位置的值,我正在尝试插入位置.表格已简化为以下内容:

CREATE TABLE value(
    Timestamp DATETIME2,
    Value float NOT NULL,
    PRIMARY KEY(Timestamp)
);

CREATE TABLE location(
    Timestamp DATETIME2,
    Position INT NOT NULL,
    PRIMARY KEY(Timestamp)
); 

INSERT INTO value VALUES 
    ('2011/12/1 16:55:01', 1),
    ('2011/12/1 16:55:02', 5),
    ('2011/12/1 16:55:05', 10),
    ('2011/12/1 16:55:08', 6);

INSERT INTO location VALUES 
    ('2011/12/1 16:55:00', 0),
    ('2011/12/1 16:55:05', 10),
    ('2011/12/1 16:55:10', 5)

预期的结果将是

TimeStamp, Value, LowerTime, LowerLocation, UpperTime, UpperLocation
2011-12-01 16:55:01,  1, 2011-12-01 16:55:00,  0, 2011-12-01 16:55:05, 10
2011-12-01 16:55:02,  5, 2011-12-01 16:55:00,  0, 2011-12-01 16:55:05, 10
2011-12-01 16:55:05, 10, 2011-12-01 16:55:05, 10, 2011-12-01 16:55:05, 10
2011-12-01 16:55:08,  6, 2011-12-01 16:55:05, 10, 2011-12-01 16:55:10,  5

(请记住,这是简化的示例数据,以便了解我尝试执行的查询.)

要进行插值,我需要计算给定值时间之前和之后的时间和位置.我目前正在使用如下查询执行此操作:

SELECT 
    V.Timestamp, 
    V.Value, 
    (SELECT MAX(Timestamp) FROM dbo.location WHERE Timestamp <= V.Timestamp) as LowerTime,
    (SELECT TOP 1 Position FROM dbo.location WHERE Timestamp <= V.Timestamp ORDER BY timestamp DESC) as LowerLocation,
    (SELECT MIN(Timestamp) FROM dbo.location WHERE Timestamp >= V.Timestamp) as UpperTime,
    (SELECT TOP 1 Position FROM dbo.location WHERE Timestamp >= V.Timestamp ORDER BY timestamp ASC) as UpperLocation
 FROM 
    dbo.value V 

现在这个有效,但这显然做了很多工作.我认为必须有一个我错过的查询简化,但我整个上午一直在玩它并且没有提出任何具体的东西.希望有人在这里有更好的主意.

我目前正在探索是否有办法找出LowerTime和UpperTime并使用它们来确定位置.就像是:

SELECT 
    V.Timestamp, 
    V.Value, 
    (SELECT MAX(Timestamp) FROM dbo.location WHERE Timestamp <= V.Timestamp) as LowerTime,
    (SELECT Position FROM dbo.location WHERE Timestamp = LowerTime) as LowerLocation,
    (SELECT MIN(Timestamp) FROM dbo.location WHERE Timestamp >= V.Timestamp) as UpperTime,
    (SELECT Position FROM dbo.location WHERE Timestamp = UpperTime) as UpperLocation
 FROM 
    dbo.value V 

但这不起作用.

EDIT1:按建议更新了查询.但是执行时间没有明显变化.

EDIT2:添加了我对目前正在尝试的方法的看法.

Answer 1

为简单起见,您至少可以使用MAX()和MIN()函数来查询timestamp字段而不是TOP 1和ORDER BY.

完整的查询将是

SELECT 
    V.Timestamp, 
    V.Value, 
    (SELECT MAX(Timestamp) FROM dbo.location WHERE Timestamp <= V.Timestamp) as LowerTime,
    (SELECT TOP 1 Position FROM dbo.location WHERE Timestamp <= V.Timestamp ORDER BY timestamp DESC) as LowerLocation,
    (SELECT MIN(Timestamp) FROM dbo.location WHERE Timestamp >= V.Timestamp) as UpperTime,
    (SELECT TOP 1 Position FROM dbo.location WHERE Timestamp >= V.Timestamp ORDER BY timestamp ASC) as UpperLocation
 FROM 
    dbo.value V