我想显示当前表中的字段和其他表中的字段但我收到错误

Question

我有三张桌子：预约，处方和药物。

约会表与处方和处方有关系与药物的关系。

我已经可以在药物表上获得药物类型的字段并显示在datagridview上。从约会表，跳到处方，然后跳到药物，以获取药物类型字​​段。

但是现在我想从约会表中再显示一个来自状态的字段，怎么做呢？

我收到了这个错误：

  

当EXISTS没有引入子查询时，只能在选择列表中指定一个表达式。

帮助。

我的表

  

    

'm'附近的语法不正确。
    'ap'附近的语法不正确。

  

private void LoadPrescriptionRecords()
{    
    //retrieve connection information info from App.config
    string strConnectionString = ConfigurationManager.ConnectionStrings["SACPConnection"].ConnectionString;
    //STEP 1: Create connection
    SqlConnection myConnect = new SqlConnection(strConnectionString);
    //STEP 2: Create command
    /*
    string strCommandText = "SELECT prescriptionID, app.aDate, med.medicationName, pat.pFirstname, pay.amount FROM PRESCRIPTION AS pres";
    strCommandText += " LEFT OUTER JOIN medication as med on pres.medicationid = med.medicationid";
    strCommandText += " LEFT OUTER JOIN appointment as app on pres.appointmentid = app.appointmentid";
    strCommandText += " LEFT OUTER JOIN patient as pat on pres.patienpaymentidtid = pat.patientid";
    strCommandText += " LEFT OUTER JOIN payment as pay on pres. = pay.paymentid";
    */
    /*
    string strCommandText = "SELECT appointmentID FROM APPOINTMENT";
    SqlCommand cmdAPPOINTMENT = new SqlCommand(strCommandText, myConnect);

    string strCommandText2 = "SELECT medicationID FROM PRESCRIPTION WHERE appointmentID IN (" + strCommandText + ")";
    SqlCommand cmdPRESCRIPTION = new SqlCommand(strCommandText2, myConnect);
    */

    string strCommandText3 = "SELECT m.medicationType, ap.appointmentID,ap.aStatus MEDICATION m, (SELECT p.medicationID, a.appointmentID,a.aStatus from APPOINTMENT a, PRESCRIPTION p WHERE a.appointmentID = p.appointmentID) ap WHERE aa.medicationID = aa.medicationID";
    //string strCommandText3 = "SELECT nFirstName FROM NURSE WHERE nurseID= (" + strCommandText2 + ")";

    myConnect.Open();

    /*
    SqlDataReader readAPPOINTMENT = cmdAPPOINTMENT.ExecuteReader();
    readAPPOINTMENT.Close();

    SqlDataReader readPRESCRIPTION = cmdPRESCRIPTION.ExecuteReader();
    readPRESCRIPTION.Close();

    SqlDataReader readMEDICATION = cmdMEDICATION.ExecuteReader();
    */ 

    PrescriptionAdapter = new SqlDataAdapter(strCommandText3, myConnect);

    //readMEDICATION.Close();
    myConnect.Close();      

    //command builder generates Select, update, delete and insert SQL
    // statements for MedicalCentreAdapter
    SqlCommandBuilder cmdBuilder = new SqlCommandBuilder(PrescriptionAdapter);
    // Empty Employee Table first
    Prescription.Clear();
    // Fill Employee Table with data retrieved by data adapter
    // using SELECT statement
    PrescriptionAdapter.Fill(Prescription);

    // if there are records, bind to Grid view & display
    if (Prescription.Rows.Count > 0)
        grdPrescription.DataSource = Prescription;         
}

Answer 1

您有两种选择：

1）修改您的查询，以便允许一组值。示例：使用IN代替=

2）修改子查询，使其只返回一行。示例：使用MAX()函数将多行减少为一行。

Answer 2

您可以执行单个查询以从多个字段中获取字段。请检查以下代码。请注意，此测试未经过测试可能需要进行一些更改。

    string strCommandText3 = "SELECT m.medicationType,ap.appointmentID,ap.aStatus FROM MEDICATION as m, (SELECT p.medicationID, a.appointmentID,a.aStatus from
APPOINTMENT a, PRESCRIPTION p WHERE a.appointmentID = p.appointmentID) ap WHERE m.medicationID = ap.medicationID ";