Question

说我有这张桌子

MyTable的

ID 的 NumValue1 的 NumValue2 的 NumValue3 的 NumValue4 的 NumValue5
1 12.17 23.97 空 0.07 空

如何使用 LINQ 语法从此单行获取 23.97 的最大值？

在SQL（MS SQL）中，我可以写这样的东西：

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

鉴于您的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));

你的行看起来像这样：

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

您可以使用此查询获取最大值：

// 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现在是23.97

如何在LINQ中获得单行中多列的最大值？

1 个答案: