怎么调用UpdateCommad来更改数据库呢

string str = inventoryText.Text;
SqlCommand sqlCmd = new SqlCommand("UPDATE " + currentTab + " SET inventory = " + str + " WHERE index =" + IndexText.Text, conn);
//sda.UpdateCommand = sqlCmd;
//sda.Update(ds.Tables[0]);
sda.UpdateCommand = sqlCmd;
sda.Update(ds.Tables[0]);
我这样写 毫无作用 想求大神指点一二