java - "Parameter index out of range (3 > number of parameters, which is 2)."更新表时

Question

我正在为大学做的期末项目需要帮助，我正在做一个图书馆类系统。我是 mySQL 的新手。

I'm having a problem on code saying, "Parameter index out of range (3 > number of parameters, which is 2)."

PreparedStatement book_edit = book_db.prepareStatement("update books set ?='?' where id=?");

            book_edit.setString(1, column); //where column is to set the column of the table
            book_edit.setString(2, input); //where input is what you want to change
            book_edit.setInt(3, book_id); //the primary key in my database

            int i = book_edit.executeUpdate();

            if (i != 0) {
                System.out.println("UPDATED!!");
            }
            else {
                System.out.println("Failed to Add Data!");
            }

Answer 1

列名不能是PreparedStatement 的变量。它必须是 SQL String 的一部分:

PreparedStatement book_edit = book_db.prepareStatement("update books set " + column + "= ? where id = ?");

book_edit.setString(1, input); //where input is what you want to change
book_edit.setInt(2, book_id); //the primary key in my database