Question

我有以下数据：

ID| TimeStamp| Data
-------------------
 1| t+1      |A
 2| t+2      |B
 3| t+3      |A
 4| t+4      |A
 5| t+5      |D

我想基于数据获取所有唯一的行。如果彼此之间有一些值，我想获取最新的值（时间戳）。

我想要的结果：

ID| TimeStamp| Data
-------------------
 1| t+1      |A
 2| t+2      |B
 4| t+4      |A
 5| t+5      |D

ID为3的行应进行过滤（t + 4> t + 3），但ID为1的行应保留（因为之间存在数据B）。

在sql / linq中查询如何？

Answer 1

您可以使用lead()进行此操作：

select id, timestamp, data
from (select t.*, lead(data) over (order by timestamp) as next_data
      from t
     ) t
where next_data <> data or next_data is null;

Answer 2

    SELECT *
    FROM your_table YT1
    WHERE NOT EXISTS (
    SELECT *
    FROM your_table YT2 yt2.data = yt1.data
        AND yt1.id = yt2.id + 1
    )

Answer 3

这是Linq的解决方案：

class Row
{
    public int Id { get; set; }
    public DateTime Timestamp { get; set; }
    public string Data { get; set; }
}

var testData = new List<Row>
{
    new Row { Id = 1, Timestamp = DateTime.Now.AddHours(-5), Data = "A" },
    new Row { Id = 2, Timestamp = DateTime.Now.AddHours(-4), Data = "B" },
    new Row { Id = 3, Timestamp = DateTime.Now.AddHours(-3), Data = "A" },
    new Row { Id = 4, Timestamp = DateTime.Now.AddHours(-1), Data = "A" },
    new Row { Id = 5, Timestamp = DateTime.Now.AddHours(-2), Data = "A" },
    new Row { Id = 6, Timestamp = DateTime.Now.AddHours(-0), Data = "D" },
};

var orderedData = testData.OrderBy(row => row.Timestamp); //The list needs to be in correct order for the where statement to work.

var filteredResult = 
    orderedData.Where((row, i) => 
        i + 1 == testData.Count || row.Data != testData[i + 1].Data); //Current row is last row OR Data of current row is different from next row.

foreach (var row in filteredResult)
{
    Console.WriteLine($"ID: {row.Id}, Timestamp: {row.Timestamp}, Data: {row.Data}");
}

基于一个属性的不同重复行

3 个答案: