2019独角兽企业重金招聘Python工程师标准>>> 
需求
如下两张表student（学生表）、score（测试成绩表）
现需要统计：2015-03-10日之后，性别 age=1 的测试成绩的 总分 与 平均分。
要求：使用一个SQL统计score表，将结果更新到student表的score_sum和score_avg字段中。
结果如图：
实现：
如果我们只需要更新一个字段，MYSQL和ORACLE语法是一样的，在 set 后面跟一个子查询即可，如下：
UPDATE student D
SET D.score_sum =
(
SELECT
SUM(B.score)
FROM score B
WHERE B.studentId = D.id
AND b.examTime >= '2015-03-10'
GROUP BY B.studentId
)
WHERE D.id =
(
SELECT
E.id FROM
(
SELECT
DISTINCT a.studentId AS id
FROM score A
WHERE A.examTime >= '2015-03-10'
) E
WHERE E.id = D.id
)
AND d.age = 1;
现在我们需要同时更新2个字段，最不经过大脑思考的方法就是 “为每个 set 后面都跟一个子查询”，
假如我们要 set 十个字段或者更多字段呢？很显然，这样在性能上是很不合适的方法。
同时更新多个字段在MYSQL和ORACLE中的方法是不一样，MYSQL需要连接表，ORACLE使用 set(...) 即可
（看了下面的SQL你会发现，还是ORACLE简单易用、易懂）
1) MYSQL 实现我们最终的需求，语句如下：
UPDATE student D
LEFT JOIN (SELECT
B.studentId,
SUM(B.score) AS s_sum,
ROUND(AVG(B.score),1) AS s_avg
FROM score B
WHERE b.examTime >= '2015-03-10'
GROUP BY B.studentId) C
ON (C.studentId = D.id)
SET D.score_sum = c.s_sum,
D.score_avg = c.s_avg
WHERE D.id =
(
SELECT
E.id FROM
(
SELECT
DISTINCT a.studentId AS id
FROM score A
WHERE A.examTime >= '2015-03-10'
) E
WHERE E.id = D.id
)
AND d.age = 1;
2) ORACLE 实现我们最终的需求，语句如下：
UPDATE student D
SET (D.score_sum, D.score_avg) = (
SELECT
SUM(B.score) AS s_sum,
ROUND(AVG(B.score),1) AS s_avg
FROM score B
WHERE b.examTime >= '2015-03-10'
AND B.studentId = D.id
GROUP BY B.studentId
)
WHERE D.id =
(
SELECT
E.id FROM
(
SELECT
DISTINCT a.studentId AS id
FROM score A
WHERE A.examTime >= '2015-03-10'
) E
WHERE E.id = D.id
)
AND d.age = 1;
本文中用到的2个知识点：
1、更新多条记录，每条记录不同值。
2、同时更新多个字段的方法。
===== 将 age = 1 并且没有测试成绩的同学给予默认值0，调整SQL如下 =====
UPDATE student D
LEFT JOIN (SELECT
B.studentId,
SUM(B.score) AS s_sum,
ROUND(AVG(B.score),1) AS s_avg
FROM score B
WHERE b.examTime >= '2015-03-10'
GROUP BY B.studentId) C
ON (C.studentId = D.id)
SET D.score_sum = IFNULL(c.s_sum,0),
D.score_avg = IFNULL(c.s_avg,0)
WHERE D.id =
(
SELECT
E.id FROM
(
SELECT
DISTINCT a.studentId AS id
FROM score A
##WHERE A.examTime >= '2015-03-10'
) E
WHERE E.id = D.id
)
AND d.age = 1;
结果如下：
Test SQL
[sql] view plain copy
- /*
- SQLyog Ultimate v10.00 Beta1
- MySQL - 5.5.28 : Database - test
- *********************************************************************
- */
- /*!40101 SET NAMES utf8 */;
- /*!40101 SET SQL_MODE=''*/;
- /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
- /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
- /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
- /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
- CREATE DATABASE /*!32312 IF NOT EXISTS*/`test` /*!40100 DEFAULT CHARACTER SET utf8 */;
- USE `test`;
- /*Table structure for table `score` */
- DROP TABLE IF EXISTS `score`;
- CREATE TABLE `score` (
- `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'ID',
- `studentId` int(11) DEFAULT NULL COMMENT '学员ID',
- `subjectName` varchar(20) DEFAULT NULL COMMENT '科目名称',
- `score` float DEFAULT NULL COMMENT '考试成绩',
- `examTime` datetime DEFAULT NULL COMMENT '考试时间',
- PRIMARY KEY (`id`)
- ) ENGINE=InnoDB AUTO_INCREMENT=25 DEFAULT CHARSET=utf8;
- /*Data for the table `score` */
- insert into `score`(`id`,`studentId`,`subjectName`,`score`,`examTime`) values (1,1,'语文',70,'2015-02-26 18:11:39'),(2,1,'数学',80,'2015-03-26 18:11:50'),(3,1,'英语',76,'2015-04-26 18:11:56'),(4,1,'历史',96,'2015-05-26 18:12:02'),(5,2,'语文\r\n数学\r\n英语\r\n历史\r\n语文',84,'2015-02-26 18:11:39'),(6,2,'数学',56,'2015-03-26 18:11:50'),(7,2,'英语',86,'2015-04-26 18:11:56'),(8,2,'历史',45,'2015-05-26 18:12:02'),(9,3,'语文',87,'2015-02-26 18:11:39'),(10,3,'数学',98,'2015-03-26 18:11:50'),(11,3,'英语',67,'2015-04-26 18:11:56'),(12,3,'历史',86,'2015-05-26 18:12:02'),(13,4,'语文',97,'2015-02-26 18:11:39'),(14,4,'数学',68,'2015-03-26 18:11:50'),(15,4,'英语',79,'2015-04-26 18:11:56'),(16,4,'历史',83,'2015-05-26 18:12:02'),(17,5,'语文',92,'2015-02-26 18:11:39'),(18,5,'数学',93,'2015-03-26 18:11:50'),(19,5,'英语',65,'2015-04-26 18:11:56'),(20,5,'历史',88,'2015-05-26 18:12:02'),(21,6,'语文',87,'2015-01-05 18:48:48'),(22,6,'数学',67,'2015-01-05 18:48:48'),(23,6,'英语',99,'2015-01-05 18:48:48'),(24,6,'历史',88,'2015-01-05 18:48:48');
- /*Table structure for table `student` */
- DROP TABLE IF EXISTS `student`;
- CREATE TABLE `student` (
- `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'ID',
- `name` varchar(20) DEFAULT NULL COMMENT '姓名',
- `score_sum` varchar(20) DEFAULT NULL COMMENT '总成绩',
- `score_avg` varchar(20) DEFAULT NULL COMMENT '平均成绩',
- `age` int(11) DEFAULT NULL COMMENT '1男0女',
- PRIMARY KEY (`id`)
- ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;
- /*Data for the table `student` */
- insert into `student`(`id`,`name`,`score_sum`,`score_avg`,`age`) values (1,'小明','252','84',1),(2,'小王','187','62.3',1),(3,'莉莉','','',0),(4,'柱子','230','76.7',1),(5,'大毛','','',0),(6,'亮子','0','0',1);
- /*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
- /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
- /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
- /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;