更新数据库问题

Question

SqlCommand cmd = new SqlCommand(string.Format("update dbo.localization set X = ' "+x+"',Y='"+y+"'  where SensorNumber = '{0}'", i), conn);
请教 更新数据库中X和Y字段更新为计算出来的x和y值，X和Y字段是float型 计算出的x和y是double类型
如上述写报错 char不能转换为float  set后应如何写？？  

Answer 1

你把数据库中的类型改为double吧

Answer 2

断点看看，最终执行的sql语句是什么，仅看这么一句，貌似没什么错误.

Answer 3

set X = ' "+x+"',Y='"+y+"'   就是把char类型的x和y赋给float类型的X和Y了  应该怎么改？

Answer 4

set X = cast('"+x+"' as float)

Answer 5

从数据类型 varchar 转换为 float 时出错。 还是不行啊

Answer 6

 for (int i = 1; i < 17; i++)
            {
                SqlCommand command1 = new SqlCommand("select * from dbo.localization where  SensorNumber ='"+i+"'", conn);
                SqlDataReader drl = command1.ExecuteReader();
                 drl.Read();
                    double d1, d2, d3, d4;
                    double x, y;
                    x = 0;
                    y = 0;
                    int d = 40;
                    int D = 30;
                    if ((!drl["RSSI1"].Equals(DBNull.Value)) &&(!drl["RSSI2"].Equals(DBNull.Value)))
                    {
                        d1 = Convert.ToDouble(drl["RSSI1"]);
                        d2 = Convert.ToDouble(drl["RSSI2"]);
                        double cosB = (d1*d1+d*d-d2*d2)/2*d1*d;
                        double sinB = Math.Sqrt(1-cosB*cosB);
                        x = cosB * d1;
                        y = sinB * d1;
                    }
                    else if ( (!drl["RSSI1"].Equals(DBNull.Value)) && (!drl["RSSI4"].Equals(DBNull.Value)))
                    {
                        d1 = Convert.ToDouble(drl["RSSI1"]);
                        d4 = Convert.ToDouble(drl["RSSI4"]);
                        double cosB = (d1*d1+D*D-d4*d4)/2*d1*D;
                        double sinB = Math.Sqrt(1-cosB*cosB);
                        x = sinB*d1;
                        y = cosB*d1;
                    }
                    else if ((!drl["RSSI3"].Equals(DBNull.Value)) && (!drl["RSSI4"].Equals(DBNull.Value)))
                    {
                        d3 = Convert.ToDouble(drl["RSSI3"]);
                        d4 = Convert.ToDouble(drl["RSSI4"]);
                        double cosB = (d4*d4+d*d-d3*d3)/2*d4*d;
                        double sinB = Math.Sqrt(1-cosB*cosB);
                        x = cosB*d4;
                        y = D - sinB*d4;
                    }
                    else if ((!drl["RSSI2"].Equals(DBNull.Value)) && (!drl["RSSI3"].Equals(DBNull.Value)))
                    {
                        d2 = Convert.ToDouble(drl["RSSI2"]);
                        d3 = Convert.ToDouble(drl["RSSI3"]);
                        double cosB = (d2*d2+D*D-d3*d3)/2*d2*D;
                        double sinB = Math.Sqrt(1-cosB*cosB);
                        x = d-sinB*d2;
                        y = cosB*d2;
                    }
                    else
                    {
                        x = 0;
                        y = 0;
                    }
                    drl.Close();                    
                    SqlCommand cmd = new SqlCommand(string.Format("update dbo.localization set X = "+x+",Y= "+y+"  where SensorNumber = '{0}'", i), conn);
                    cmd.ExecuteNonQuery();
                    
                }
代码写的比较乱  见笑  X和Y 数据库中定义的是float型的

Answer 7

如果实在不知道怎么格式化数据格式，可以由SqlParameter自动进行格式化处理。
手动拼字符串还要做参数安全性检查，比较麻烦。