如何在LINQ中获得单列中多列的最大值？

Question

说我有这个表

MyTable的

ID         NumValue1       NumValue2       NumValue3       NumValue4       NumValue5
        12.17                             23.97                               空                                   0.07                               空

如何获得这23.97使用LINQ语法此单列最大值？

在SQL（MS SQL），我可以写这样的事：

SELECT MaxNum = case 
when MyTable.NumValue1 is not null and 
(MyTable.NumValue1 >= MyTable.NumValue2 or MyTable.NumValue2 is null) and 
(MyTable.NumValue1 >= MyTable.NumValue3 or MyTable.NumValue3 is null) and 
(MyTable.NumValue1 >= MyTable.NumValue4 or MyTable.NumValue4 is null) and 
(MyTable.NumValue1 >= MyTable.NumValue5 or MyTable.NumValue5 is null) 
then MyTable.NumValue1 
when MyTable.NumValue2 is not null and 
(MyTable.NumValue2 >= MyTable.NumValue1 or MyTable.NumValue1 is null) and 
(MyTable.NumValue2 >= MyTable.NumValue3 or MyTable.NumValue3 is null) and 
(MyTable.NumValue2 >= MyTable.NumValue4 or MyTable.NumValue4 is null) and 
(MyTable.NumValue2 >= MyTable.NumValue5 or MyTable.NumValue5 is null) 
then MyTable.NumValue2 
when MyTable.NumValue3 is not null and 
(MyTable.NumValue3 >= MyTable.NumValue1 or MyTable.NumValue1 is null) and 
(MyTable.NumValue3 >= MyTable.NumValue2 or MyTable.NumValue2 is null) and 
(MyTable.NumValue3 >= MyTable.NumValue4 or MyTable.NumValue4 is null) and 
(MyTable.NumValue3 >= MyTable.NumValue5 or MyTable.NumValue5 is null) 
then MyTable.NumValue3 
when MyTable.NumValue4 is not null and 
(MyTable.NumValue4 >= MyTable.NumValue1 or MyTable.NumValue1 is null) and 
(MyTable.NumValue4 >= MyTable.NumValue2 or MyTable.NumValue2 is null) and 
(MyTable.NumValue4 >= MyTable.NumValue3 or MyTable.NumValue3 is null) and 
(MyTable.NumValue4 >= MyTable.NumValue5 or MyTable.NumValue5 is null) 
then MyTable.NumValue4 
when MyTable.NumValue5 is not null and 
(MyTable.NumValue5 >= MyTable.NumValue1 or MyTable.NumValue1 is null) and 
(MyTable.NumValue5 >= MyTable.NumValue2 or MyTable.NumValue2 is null) and 
(MyTable.NumValue5 >= MyTable.NumValue3 or MyTable.NumValue3 is null) and 
(MyTable.NumValue5 >= MyTable.NumValue4 or MyTable.NumValue4 is null) 
then MyTable.NumValue5 
else null 
end 
FROM MyTable WHERE MyTable.ID=1; 

谢谢。

Answer 1

鉴于你DataTable看起来像这样：

var t = new DataTable(); 
t.Columns.Add("ID", typeof(Int32)); 
t.Columns.Add("NumValue1", typeof(decimal)); 
t.Columns.Add("NumValue2", typeof(decimal)); 
t.Columns.Add("NumValue3", typeof(decimal)); 
t.Columns.Add("NumValue4", typeof(decimal)); 
t.Columns.Add("NumValue5", typeof(decimal)); 

和你的行看起来是这样的：

// get all values: 
var max = row.ItemArray 
      // only values that are not DBNull: 
      .Where(o => o != DBNull.Value) 
        // convert to decimal and get the max value: 
        .Max(o => Convert.ToDecimal(o)); 

max：

var row = t.Rows.Add(new object[] {1, 
            12.17m, 
            23.97m, 
            DBNull.Value, 
            0.07m, 
            DBNull.Value}); 

你可以用这个查询得到最大的价值现在是23.97