如何使用netbeans计算数据库语句

Question

我正在尝试计算输入并将其与数据库中的数据字段进行匹配，然后计算状态并显示输入借来的图书数量。

        Statement statement = conn.createStatement();

        String sql = "SELECT COUNT(jtfMemberID.getText()) as num FROM LOAN WHERE LOAN_STATUS='BORROWED'";

        ResultSet rs1 = statement.executeQuery(sql); 
        int personCount = 0; 

        if(rs1.next()) { 
            personCount = rs1.getInt("num");
            jlbBookBorrow.setText(rs1.getString(personCount));
        }else{
            jlbBookBorrow.setText("0");
        }

Answer 1

文字jtfMemberID.getText()将按照SQL String的字面解释。你需要把它解压出来：

String sql = "SELECT COUNT(" + jtfMemberID.getText() + ") as num FROM LOAN WHERE LOAN_STATUS='BORROWED'";

另外，为防止SQL Injection攻击，请考虑使用PreparedStatement。