在另一个查询中使用 SQL 查询结果

Question

所以我正在用名称列表填充一个组合框。现在单击其中一个名称后，我执行

SELECT Id FROM FIRSTTABLE WHERE Name ='" + ClientComboBox.Text + "'

现在我想获取该 ID 并在 SECONDTABLE 中执行另一个 Sql 查询。但是，在那个 SECONDTABLE Id 中称为 ClientId。另外我只想填充一次datagridview。所以我不想显示FIRSTTABLE结果，只显示我从SECONDTABLE结果中得到的结果。不确定这一切是否有意义，所以如果您有任何问题，请告诉我。

private void ClientComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {

            var myConnection = new SqlConnection(DBConnectionBox.Text);
            //myConnection.Open();


            var Cmd = new SqlCommand("SELECT Id FROM FIRSTTABLE WHERE Name ='" + ClientComboBox.Text + "';");
            Cmd.Connection = myConnection;
            Cmd.CommandType = CommandType.Text;

            var Cmd2 = new SqlCommand("SELECT * FROM SECONDTABLE WHERE ClientId ='"+"';");
            Cmd2.Connection = myConnection;
            Cmd2.CommandType = CommandType.Text;

            SqlDataAdapter sqlDataAdap = new SqlDataAdapter(Cmd);
            SqlDataAdapter sqlDataAdap2 = new SqlDataAdapter(Cmd2);

            DataTable dtRecord = new DataTable();
            DataTable dtRecord2 = new DataTable();

            sqlDataAdap.Fill(dtRecord);
            sqlDataAdap2.Fill(dtRecord2);

            ClientInfoDGV.DataSource = dtRecord;
            ClientInfoDGV.DataSource = dtRecord2;
        }

Answer 1

听起来你想使用内连接。

var Cmd = new SqlCommand(@"SELECT Id, SECONDTABLE.* FROM FIRSTTABLE
   JOIN SECONDTABLE ON FIRSTTABLE.Id = SECONDTABLE.ClientId  
   WHERE Name ='" + ClientComboBox.Text + "';")

Answer 2

像这样在单个查询中

SELECT * 
FROM   secondtable 
WHERE  clientid IN (SELECT f.id 
                    FROM   firsttable f
                    WHERE  f.NAME = "clientcombobox.text") 

或Exists（首选）

SELECT * 
FROM   secondtable s 
WHERE  EXISTS(SELECT 1 
              FROM   firsttable f 
              WHERE  s.clientid = f.id 
                     AND f.NAME = "clientcombobox.text")