C#代码小问题

private void BasicallySearch()
        {
            string sql = "";
            // 查询语句的前半部分
            sql = "SELECT Id,NickName,Age,Sex FROM Users";
           
            // 精确查找
            if (rdoNicetySearch.Checked == true)
            {
                if (txtLoginId.Text.Trim() == "" && txtNickName.Text.Trim() == "")
                {
                    MessageBox.Show("还没有填查询条件呢！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    return;
                }
                // 按帐号查找
                else if (txtLoginId.Text.Trim() != "") 
                {
                    sql += string.Format(" WHERE Id={0}", int.Parse(txtLoginId.Text.Trim()));
                }
                // 按昵称查找
                else
                {
                    sql += string.Format(" WHERE NickName like '%{0}%'", txtNickName.Text.Trim());
                 }               
            }
           
            // 重新填充DataSet
            dataSet.Tables[0].Clear();
            dataAdapter.SelectCommand.CommandText = sql;
            dataAdapter.Fill(dataSet,"Users");

            // 设置控件可见的属性
            // 调整显示结果的panel的位置，让它和显示条件的Panel的位置相同
            pnlBaseResult.Location = pnlBaseCondition.Location;
            // 使显示结果的panel可见
            pnlBaseResult.Visible = true;
            btnAdd.Visible = true;　　//“加为好友”按钮可见
            btnBack.Visible = true;   //“上一步”按钮可见
        }

这个代码的意思：dataAdapter.SelectCommand.CommandText = sql;

和dataAdapter.CommandText = sql;意思一样不，有什么区别

补充：dataAdapter.CommandText = sql;
就是sd.CommandText = sql;
笔误都没看都来，晕，
你直接说sd.CommandText = sql;和
sd.SelectCommand.CommandText = sql;
有什么不同

追问：我要在下拉框显示血型和星座，要写2行查询的代码就要用它。
dataAdapter.CommandText = sql;
如：
string sql="";
sql="select star from star"; //查星座
class1.con.Open();
sqlcommand sm=new sqlcommand(sql,class1.con);
sqlDataRead sd=sm.Executereader();
while(sd.Read())
{
ComboBox1.Items.Add(sd[0].Tostring());
}
sd.close();
sql="select getbood where getbood";//查血型
dataAdapter.CommandText = sql;
sd=sm.ExecuteReader();
while(sd.Read())
{
ComboBox2.Items.Add(sd[0].Tostring());
}
sd.close();
class1.con.close();
 
 

答案：        private void button1_Click(object sender, EventArgs e)
        {
            dataGridView1.Visible = true;
            if (radioButton1.Checked == true && tabControl1.SelectedIndex == 0) //精确查找好友
            {
                panel1.Visible = false;
                if (yanzheng())
                {
                    button3.Visible = true;
                    button4.Visible = true;
                    pictureBox1.Visible = true;
                    if (txtId.Text.Trim() == "<请输入对方数字帐号>") 
                    {
                        txtId.Text = "";
                    }
                    if (txtNickName.Text.Trim() == "<请输入对方昵称>") 
                    {
                        txtNickName.Text = "";
                    }
                    string sql = "select id,nickname,sex,age,faceId,FriendshipPolicyId from users ";
                    if (txtId.Text.Trim() != "" && txtNickName.Text.Trim() != "")
                    {
                        sql = sql + string.Format("where id={0} and nickname like '{1}'", txtId.Text.Trim(),txtNickName.Text.Trim());
                    }
                    else if (txtId.Text.Trim() != "" && txtNickName.Text.Trim() == "") 
                    {
                        sql = sql + string.Format("where id='{0}'",txtId.Text.Trim());
                    }
                    else if (txtId.Text.Trim() == "" && txtNickName.Text.Trim() != "") 
                    {
                        sql = sql + string.Format("where nickname like '{0}'",txtNickName.Text.Trim());
                    }
                    ds = DBHelper.GetDataSet(sql, "user");
                    dataGridView1.DataSource = ds.Tables["user"];
                    if (ds.Tables["user"].Rows.Count < 1)
                    {
                        pictureBox2.Visible = true;
                    }
                }
                else
                {
                    dataGridView1.Visible = false;
                    txtId.Visible = true;
                    txtNickName.Visible = true;
                    SearchFriendFrom1 sh1 = new SearchFriendFrom1();
                    sh1.ShowDialog();
                }
            }
            if(radioButton2.Checked==true&&tabControl1.SelectedIndex==0)  //按条件查找好友
            {
                button3.Visible = true;
                button4.Visible = true;
                pictureBox1.Visible = true;
                panel1.Visible = true;
                string sql = "select id,nickname,sex,age,faceId,FriendshipPolicyId from users ";
                if (comboBox1.SelectedIndex == 0 && comboBox2.SelectedIndex == 0) 
                {
                    sql = sql;
            

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