需求
如下兩張表student(學生表)、score(測試成績表)
現需要統計:2015-03-10日之後,性別 age=1 的測試成績的 總分 與 平均分。
要求:使用一個SQL統計score表,將結果更新到student表的score_sum和score_avg字段中。
結果如圖:
實現:
如果我們只需要更新一個字段,MYSQL和ORACLE語法是一樣的,在 set 後面跟一個子查詢即可,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;
現在我們需要同時更新2個字段,最不經過大腦思考的方法就是 “為每個 set 後面都跟一個子查詢”,
假如我們要 set 十個字段或者更多字段呢?很顯然,這樣在性能上是很不合適的方法。
同時更新多個字段在MYSQL和ORACLE中的方法是不一樣,MYSQL需要連接表,ORACLE使用 set(...) 即可
(看了下面的SQL你會發現,還是ORACLE簡單易用、易懂)
1) MYSQL 實現我們最終的需求,語句如下:
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 實現我們最終的需求,語句如下:
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個知識點:
1、更新多條記錄,每條記錄不同值。
2、同時更新多個字段的方法。
========================將 age = 1 ,沒有測試成績的同學給予默認值0,調整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;
結果如下:
Test SQL
/* 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 '學員ID', `subjectName` varchar(20) DEFAULT NULL COMMENT '科目名稱', `score` float DEFAULT NULL COMMENT '考試成績', `examTime` datetime DEFAULT NULL COMMENT '考試時間', 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,'語文',70,'2015-02-26 18:11:39'),(2,1,'數學',80,'2015-03-26 18:11:50'),(3,1,'英語',76,'2015-04-26 18:11:56'),(4,1,'歷史',96,'2015-05-26 18:12:02'),(5,2,'語文\r\n數學\r\n英語\r\n歷史\r\n語文',84,'2015-02-26 18:11:39'),(6,2,'數學',56,'2015-03-26 18:11:50'),(7,2,'英語',86,'2015-04-26 18:11:56'),(8,2,'歷史',45,'2015-05-26 18:12:02'),(9,3,'語文',87,'2015-02-26 18:11:39'),(10,3,'數學',98,'2015-03-26 18:11:50'),(11,3,'英語',67,'2015-04-26 18:11:56'),(12,3,'歷史',86,'2015-05-26 18:12:02'),(13,4,'語文',97,'2015-02-26 18:11:39'),(14,4,'數學',68,'2015-03-26 18:11:50'),(15,4,'英語',79,'2015-04-26 18:11:56'),(16,4,'歷史',83,'2015-05-26 18:12:02'),(17,5,'語文',92,'2015-02-26 18:11:39'),(18,5,'數學',93,'2015-03-26 18:11:50'),(19,5,'英語',65,'2015-04-26 18:11:56'),(20,5,'歷史',88,'2015-05-26 18:12:02'),(21,6,'語文',87,'2015-01-05 18:48:48'),(22,6,'數學',67,'2015-01-05 18:48:48'),(23,6,'英語',99,'2015-01-05 18:48:48'),(24,6,'歷史',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 '總成績', `score_avg` varchar(20) DEFAULT NULL COMMENT '平均成績', `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 */;