java - 如何使用用户输入作为查询参数？

Question

所以我对 java 和 SQL 非常陌生，它们是我的第一个编程语言。我正在尝试使用 JDBC 做一些工作。我想允许用户输入 id 并根据变量返回查询。如果有人至少能指出我正确的方向......这是我开始的代码。请注意，它很粗糙，但只是想获得一段工作代码，以便我可以更好地在我的主类中实现它。

 Scanner input = new Scanner(System.in);
    Class.forName("org.sqlite.JDBC");
    Connection conn =
            DriverManager.getConnection("jdbc:sqlite:C:\\Users\\Derek\\Documents\\Databases\\example.sqlite");
    Statement stat = conn.createStatement();
    PreparedStatement prep1 = conn.prepareStatement(
            "insert into MedType values (?, ?);");
    PreparedStatement prep2 = conn.prepareStatement(
            "insert into Media values (?, ?,?, ?,?, ?);");

    System.out.print("Please choose a database(MedType or Media): ");
    String db=input.next();

    if(db.equalsIgnoreCase("MedType"))
    {
    System.out.print("Enter in ID: ");
    String answer1 = input.next();

    System.out.print("");
    String answer2 = input.nextLine();

    System.out.print("Enter in Description: ");
    String answer3 = input.nextLine();

    prep1.setString(1, answer1);//add values into cell
    prep1.setString(2, answer3);
    prep1.addBatch();//add the columns that have been entered

    }
conn.setAutoCommit(false);
    prep1.executeBatch();
    prep2.executeBatch();
    conn.setAutoCommit(true);




    System.out.print("Please Enter Query(One or All): ");
    String q=input.next();


    ResultSet rs= stat.executeQuery("select * from MedType;");


    if(q.equalsIgnoreCase("all")){
    while (rs.next()) {
        System.out.print("All ID = " + rs.getString("ID") + " ");
        System.out.println("All Description = " + rs.getString("Description"));}
    }
   if(q.equalsIgnoreCase("one")){
         System.out.print("Enter ID: ");

    }
   int idNum=input.nextInt();
    ResultSet oneRs = stat.executeQuery("select * from MedType Where"+ (rs.getString("ID")+"="+idNum));

   if(q.equalsIgnoreCase("one")){


        while (oneRs.next()) {
            System.out.print("ID = " + oneRs.getString("ID") + " ");
            System.out.println("Description = " + oneRs.getString("Description"));
        }
    }

    rs.close();
    oneRs.close();
    conn.close();

}
}

ResultSet oneRs = stat.executeQuery("select * from MedType Where"+
   (rs.getString("ID")+"="+idNum));

这就是我遇到麻烦的地方。创建一条语句，表示如果表的 id 等于用户输入，则从表中返回某些内容。我收到此错误

线程“main”java.sql.SQLException中出现异常:[SQLITE_ERROR] SQL错误或丢失数据库(靠近“=”:语法错误)

Answer 1

在查询中，您尝试通过传递 id 来访问单行。在一般的 sql 查询中，我们使用通过传递一些信息来访问单行。 select * from MedType where id=3 此查询将返回包含 id 等于 3 的行的结果集。 因此，在您的代码中，如果您的数据库 id 列是 int，则您的查询应该是 select * from MedType where id="+idNum+" 。 并仅将此查询保留在 if block 中，即

 if(q.equalsIgnoreCase("one"))
{
         System.out.print("Enter ID: ");
         int idNum=input.nextInt();
    ResultSet oneRs = stat.executeQuery("select * from MedType Where id="+idNum+" ");
    // if id column in db is int if it is string then use id='"+idNum+"'                                            

        while (oneRs.next())
       {
            System.out.print("ID = " + oneRs.getString("ID") + " ");
            System.out.println("Description = " + oneRs.getString("Description"));
        }
 }