Invalid usage of aggregate function Sum() and Type: String

Question

I have a data table and a column contains int values. I have not specified the column with any datatype. When I perform the following.

object sum = dttest.Co         


        

Answer 1

When the program try it sum a datatable column which declared as string this error occur.
Use the below code to make compute operation on string column.

dtTable.Compute("Sum(Convert(" + col_Name + ", 'System.Int32')",""); 

Answer 2

You can use LINQ to Datatable:

 var result = dttest.AsEnumerable()
                    .Sum(x => Convert.ToInt32(x["Value"]));

Example how to Sum for specific name:

 var result = dttest.AsEnumerable()
                    .Where(r => r.Field<string>("Name") == "FilterName")
                    .Sum(x => Convert.ToInt32(x["Value"]));

Answer 3

try

dttest.Compute("Sum(Convert([Value], 'System.Int32'))","[Value] IS NOT NULL");

Answer 4

try

object sum = dttest.Compute("Sum(Value)", "[Value] IS NOT NULL");

Sample code

    static DataTable GetTable()
    {
        DataTable table = new DataTable();
        table.Columns.Add("Value", typeof(int));
        table.Columns.Add("Name", typeof(string));
        table.Rows.Add(null, "a");
        table.Rows.Add(50, "a");
        table.Rows.Add(10, "a");
        table.Rows.Add(21, "b");
        table.Rows.Add(100, "b");
        return table;
    }
    static void Main(string[] args)
    {
        DataTable dt =GetTable();
        var str = dt.Compute("Sum(Value)", "Name='a' and Value is not null");
    }

You can't Call Sum with Convert, but you can try below

DataTable dt =GetTable();
dt.Columns.Add("temp", typeof(int), "Convert(Value, 'System.Int32')");
var str = dt.Compute("Sum(temp)", "Name='a' and Value is not null");