Question

用户输入疾病，SQL应该返回患有该疾病的所有患者详细信息。但是我收到了以下错误：

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?' at line 1

SQL Query如下所示。请帮我调试一下。

SELECT patient_personal_details.patient_id, 
       patient_personal_details.first_name, 
       patient_personal_details.last_name, 
       patient_personal_details.gender, 
       patient_personal_details.occupation, 
       patient_personal_details.marital_status 
FROM patient_personal_details
INNER JOIN patient_medical_details
ON patient_personal_details.patient_id = patient_medical_details.patient_id
WHERE patient_medical_details.disease = ?

以下是代码：

public JTable getAllPatientsByDisease(String disease)throws RemoteException{
    JTable table = null;
    try{
        Class.forName("com.mysql.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost/hospital_database","root","");
        String sql = " SELECT patient_personal_details.patient_id, patient_personal_details.first_name, patient_personal_details.last_name, patient_personal_details.gender, patient_personal_details.occupation, patient_personal_details.marital_status FROM patient_personal_details "
                + " INNER JOIN patient_medical_details "
                + " ON patient_personal_details.patient_id = patient_medical_details.patient_id "
                + " WHERE patient_medical_details.disease = ? ";
        PreparedStatement ps = con.prepareStatement(sql);
        ps.setString(1, disease);
        ResultSet rs = ps.executeQuery(sql);

        table =  new JTable(buildTableModel(rs));
    }
    catch(SQLException | ClassNotFoundException e){
        System.out.println("Error: "+e);
    }
    return table;
}

Answer 1

更新了答案：（现在我们有了代码）

问题在于：

ResultSet rs = ps.executeQuery(sql);
// ----------------------------^^^

删除sql，只需使用：

ResultSet rs = ps.executeQuery();

通过将SQL指定为参数，您使用的是Statement#executeQuery，而不是PreparedStatement#executeQuery。 Statement#executeQuery按字面意思使用SQL字符串，而不替换参数（基本上就像你没有调用setString）。（是的，这不是JDBC人员梦寐以求的设计决定。）

原始答案：

该错误消息的关键位是“... near'？'”这告诉我们您从未在该点设置要替换为查询的值，所以？用字面意思。

您需要使用setString（如果“疾病”列是文本列）或setInt等来设置查询的参数。 E.g：

PreparedStatement ps = connection.prepareStatement("SELECT ... WHERE patient_medical_details.disease = ?");
ps.setString(1, "arachnophobia"); // <===
ResultSet rs = ps.executeQuery();

参数编号（有点令人惊讶）从第一个?开始为1，第二个开始为2，等等。

SQL语句和准备语句错误

1 个答案: