小编use*_*466的帖子

我不知道为什么我得到上述异常,请有人看看它....

DataTable DataTable_Time = new DataTable("Star_Schema__Dimension_Time");

DataColumn Sowing_Day = new DataColumn();
Sowing_Day.ColumnName = "Sowing_Day";

DataColumn Sowing_Month= new DataColumn();
Sowing_Month.ColumnName = "Sowing_Month";      

DataColumn Sowing_Year = new DataColumn();
Sowing_Year.ColumnName = "Sowing_Year";

DataColumn Visit_Day= new DataColumn();
Visit_Day.ColumnName = "Visit_Day";

DataColumn Visit_Month = new DataColumn();
Visit_Month.ColumnName = "Visit_Month";

DataColumn Visit_Year = new DataColumn();
Visit_Year.ColumnName = "Visit_Year";

DataColumn Pesticide_spray_day = new DataColumn();
Pesticide_spray_day.ColumnName = "Pesticide_spray_day";

DataColumn Pesticide_spray_Month = new DataColumn();
Pesticide_spray_Month.ColumnName = "Pesticide_spray_Month";

DataColumn Pesticide_spray_Year = new DataColumn();
Pesticide_spray_Year.ColumnName = "Pesticide_spray_Year";

DataTable_Time.Columns.Add(Pesticide_spray_Year);
DataTable_Time.Columns.Add(Sowing_Day);
DataTable_Time.Columns.Add(Sowing_Month);
DataTable_Time.Columns.Add(Sowing_Year); …

我有一个表有2列,即FarmerName,PesticideUsed和Town.

1. 我怎样才能找到使用特定农药的农民平均数.
2. 每个城镇的平均农民人数

有29个独特的农药和8个独特的城镇.

我试着写第一个即ie

adapter.SelectCommand = new SqlCommand(
    "select count(FarmerName)/29 as average_count from try", con);

我不认为这是对的.

我怎么会这样做....