小编sem*_*kin的帖子

我在MySql数据库中有一个表PAYMENTS:

CREATE TABLE `PAYMENTS` (
    `ID` BIGINT(20) NOT NULL AUTO_INCREMENT,
    `USER_ID` BIGINT(20) NOT NULL,
    `CATEGORY_ID` BIGINT(20) NOT NULL,
    `AMOUNT` DOUBLE NULL DEFAULT NULL,
    PRIMARY KEY (`ID`),
    INDEX `PAYMENT_INDEX1` (`USER_ID`),
    INDEX `PAYMENT_INDEX2` (`CATEGORY_ID`),
    INDEX `PAYMENT_INDEX3` (`CATEGORY_ID`, `USER_ID`)
) ENGINE=InnoDB;

我想获得ech类别中每个用户的汇总金额.这是脚本:

select sum(AMOUNT), USER_ID, CATEGORY_ID
from PAYMENTS
group by USER_ID, CATEGORY_ID;

MySql的EXPLAIN命令显示Extra:"Using temporary; Using filesort"

如何摆脱使用临时&filesort？