项目需求：统计出会计总账中要显示的数据，即：每月每一科目下，借方总额，贷方总额等分别是多少
详细步骤：查询凭证明细表，根据科目，时间分类，得出统计数据。
考虑到数据库好忘Oracle数据库迁移，（oracle中group by必须加入所有select列出的字段,统计字段除外。）
写成这样：
String sql = "select accountTitle, year(voucher.voucherDate) as y," + "month(voucher.voucherDate) as m,sum(debitMoney),sum(creditMoney) " + "from RecordingVoucherDetail"+ " group by accountTitle,year(voucher.voucherDate),month(voucher.voucherDate)";
但，报空指针异常，不知道为什么不能正确执行。
将from 改成 fromRecordingVoucherDetail as t 就查出来了。
String sql = "select t.accountTitle, year(t.voucher.voucherDate) as y," + "month(t.voucher.voucherDate) as m,sum(t.debitMoney),sum(t.creditMoney) " + "from RecordingVoucherDetail as t"+ " group by t.accountTitle,year(t.voucher.voucherDate),month(t.voucher.voucherDate)";
