如何在for循环中执行准备好的语句以从jsp中的表中获取数据？

索努·加德瓦

这段代码有什么问题？我收到此错误。

java.sql.SQLSyntaxErrorException: 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 'attendance where sub_id='3' and reg_no='1111'' at line 1

代码

try {
    Class.forName("com.mysql.jdbc.Driver");
    Connection con =
            DriverManager.getConnection("jdbc:mysql://localhost:3306/sms", "root", "*****");

    int k;
    String sub = "";
    int t_class[] = new int[counter];
    int att_class[] = new int[counter];
    int tallo_class[] = new int[counter];

    PreparedStatement ps3;
    PreparedStatement ps4;
    PreparedStatement ps5;

    for (k = 0; k < (counter - 1); k++) {

        sub = subjects_id[k];

        //START : getting total no of classes held 
        ps3 = con.prepareStatement("SELECT COUNT(*) FORM attendance where sub_id=? and reg_no=?");

        ps3.setString(1, sub);
        ps3.setString(2, reg_no);

        ResultSet rs3 = ps3.executeQuery();

        rs3.next();
        t_class[k] = rs3.getInt(1);
    }
}

萨姆·奥罗斯科

所以一个重要的提示是你希望prepare你的语句在循环之外。这就是准备它的重点（另外，参数化输入）。您可以重复使用该语句，然后如上所述您拼错了单词FROM。

PreparedStatement statement = con.prepareStatement("SELECT COUNT(*) FROM attendance where sub_id=? and reg_no=?");
        for (int i = 0; i < (k - 1); i++) {
            statement.setString(1, sub);
            statement.setString(2, reg_no);
            ResultSet rs3 = ps3.executeQuery();
            rs3.next();
            t_class[k] = rs3.getInt(1);
        }

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