技術標籤：sql資料庫mysqlsql

文章目錄

• 範圍分組
• • 需求說明
  • 示例
  • • sum 與 case when組合
• 類別值分組
• • 需求說明
  • 示例
  • • group by 、 sum 與 case when組合

本文主要介紹mysql常用的兩種分組情況：

• 按數值範圍分組，並橫向展示
• 按類別值分組，並橫向展示

PS：為直觀展示，最後橫向展示的欄位名包含中文（真實場景中不推薦使用！！！）

範圍分組

需求說明

1. 對總分範圍進行統計，示例如下

2. 希望將上述分組後的結果，變更為橫向展示，如未及格、D、C、B、A級別各多少人

示例

1. 建立表及資料

CREATE TABLE `t_student` (
	`id` INT(11) NOT NULL AUTO_INCREMENT COMMENT 'PK',
	`score` INT(11) NOT NULL DEFAULT '0',
	`name` VARCHAR(64) NOT NULL COLLATE 'utf8mb4_unicode_ci',
	PRIMARY KEY (`id`) USING BTREE
) COMMENT='學生表' COLLATE='utf8mb4_unicode_ci' ENGINE=InnoDB AUTO_INCREMENT
 
=1;

INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (1, 58, '王一');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (2, 63, '趙一');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (3, 68, '李一');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (4, 71, '德康');
INSERT INTO `t_student`
 
 (`id`, `score`, `name`) VALUES (5, 77, '古月');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (6, 75, '劉一');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (7, 89, '李二');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (8, 89, '李三');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (9, 88, '李四');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (10, 86, '李武');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (11, 100, '張三');
INSERT INTO `t_student` (`id`, `score`, `name`) VALUES (12, 95, '王五');

2. 分組及橫向展示

SELECT 
	sum(case when `score` < 60 then 1 ELSE 0 END) AS '不及格',
	sum(case when `score` < 70 AND `score` >= 60 then 1 ELSE 0 END) AS D,
	sum(case when `score` < 80 AND `score` >= 70 then 1 ELSE 0 END) AS C,
	sum(case when `score` < 90 AND `score` >= 80 then 1 ELSE 0 END) AS B,
	sum(case when `score` <= 100 AND `score` >= 90 then 1 ELSE 0 END) AS A
FROM t_student 

sum 與 case when組合

一般使用case when進行範圍區分（簡要分組），再利用count進行統計

類別值分組

需求說明

1. 對類別進行統計，示例如下

2. 希望將上述分組後的結果，變更為橫向展示，如選擇語文、數學、英語及體育各多少人

示例

1. 建立表及資料

CREATE TABLE `t_course` (
	`id` INT(11) NOT NULL AUTO_INCREMENT,
	`type` INT(11) NOT NULL COMMENT '型別（0：語文；1：數學；2：英語；3：體育）',
	`student_id` INT(11) NOT NULL COMMENT '學生id',
	PRIMARY KEY (`id`) USING BTREE
) COMMENT='課程表' COLLATE='utf8mb4_unicode_ci' ENGINE=InnoDB;

INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (1, 0, 1);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (2, 0, 2);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (3, 0, 3);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (4, 0, 4);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (5, 1, 1);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (6, 1, 3);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (7, 2, 1);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (8, 2, 2);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (9, 2, 4);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (10, 3, 1);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (11, 3, 2);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (12, 3, 3);
INSERT INTO `t_course` (`id`, `type`, `student_id`) VALUES (13, 3, 4);

2. 用group by 對類別進行分組

SELECT `type`, COUNT(*) AS counts FROM t_course GROUP BY `type` 

3. 將分組後的縱向結果，換為橫向展示

SELECT 
	SUM(case when t.`type` = 0 then t.counts ELSE 0 END) AS '語文',
	SUM(case when t.`type` = 1 then t.counts ELSE 0 END) AS '數學',
	SUM(case when t.`type` = 2 then t.counts ELSE 0 END) AS '英語',
	SUM(case when t.`type` = 3 then t.counts ELSE 0 END) AS '體育'
FROM 
(
	SELECT 
		`type`, COUNT(*) AS counts 
	FROM t_course 
	GROUP BY `type` 
)t

group by 、 sum 與 case when組合

分組統計：

• group by 分組 count 個數
• case when 按條件區分，sum求和