从数据库c sharp中选择第5个条目

Question

Im trying to sort a database table then select the 5th entry.

I have got the code below but this dosnt seem to give me the correct value Can anyone help please?

OleDbCommand com12 = new OleDbCommand(@"SELECT TOP 5 [Flight_Date] 
                                        FROM Flights 
                                        WHERE [Claimed_By_ID] = ? 
                                         AND [Flight_Date] <= ?
                                         AND [Flight_Date] >= ? 
                                        ORDER BY [Flight_Date] DESC", Program.DB_CONNECTION);
com12.Parameters.Add(new OleDbParameter("", p.ID));
com12.Parameters.Add(new OleDbParameter("", DateTime.Today));
com12.Parameters.Add(new OleDbParameter("", DateTime.Today.AddMonths(-6)));
OleDbDataReader dr12 = com12.ExecuteReader();

Answer 1

You can wrap your query in another query:

SELECT MIN([Flight_Date]) AS [Flight_Date_5]
FROM (SELECT TOP 5 [Flight_Date] 
      FROM Flights 
      WHERE [Claimed_By_ID] = ? 
       AND [Flight_Date] <= ?
       AND [Flight_Date] >= ? 
      ORDER BY [Flight_Date] DESC) AS [Top5]

This will just return the 5th highest entry. If there are fewer than 5 total entries, it will return the lowest of them.

Answer 2

Use a DataTable , fill it with your reader then get the fifth record with LINQ :

DataTable dt = new DataTable();
dt.Load(com12.ExecuteReader());
var fifthRow = dt.AsEnumerable().Skip(4).First();

Answer 3

UPDATE:

Sorry this is SQL Server ONLY. It won't work for MYSQL.

Use a CTE is another correct way:

WITH AllData AS
(
SELECT TOP 5 ROW_NUMBER() OVER (order by [Flight_Date] DESC) as RowNumber
      FROM Flights 
      WHERE [Claimed_By_ID] = ? 
       AND [Flight_Date] = ? 
)
SELECT * FROM AllData WHERE RowNumber = 5

If there aren't 5 rows, it will return nothing.

Answer 4

MySQL doesn't have TOP . Use LIMIT ...

SELECT [Flight_Date] 
    FROM Flights 
    WHERE [Claimed_By_ID] = ? 
     AND [Flight_Date] <= ?
     AND [Flight_Date] >= ? 
    ORDER BY [Flight_Date] DESC
    LIMIT 4, 1