MYSQL GROUP_CONCAT函數

原創

qq_40202111

2020-02-21 07:53

mysql 中 group_concat() 函數完整語法

group_concat([DISTINCT] 要連接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])

例子一：

創建數據庫，並插入數據

-- ----------------------------
-- Table structure for score
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `id` int(11) NOT NULL,
  `score` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of score
-- ----------------------------
INSERT INTO `score` VALUES ('1', '10');
INSERT INTO `score` VALUES ('1', '20');
INSERT INTO `score` VALUES ('1', '30');
INSERT INTO `score` VALUES ('2', '20');
INSERT INTO `score` VALUES ('2', '30');
INSERT INTO `score` VALUES ('2', '40');
INSERT INTO `score` VALUES ('3', '30');
INSERT INTO `score` VALUES ('3', '40');
INSERT INTO `score` VALUES ('3', '40');

效果如下圖：

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執行如下sql 語句：
SELECT id,GROUP_CONCAT(score) from score GROUP BY id;

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SELECT id,GROUP_CONCAT(DISTINCT score) from score GROUP BY id;

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SELECT id,GROUP_CONCAT(DISTINCT score ORDER BY score DESC) from score GROUP BY id;

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SELECT id,GROUP_CONCAT(DISTINCT score ORDER BY score DESC SEPARATOR ";") from score GROUP BY id;

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例子二：

創建表，並插入數據

-- ----------------------------
-- Table structure for grade1
-- ----------------------------
DROP TABLE IF EXISTS `grade1`;
CREATE TABLE `grade1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `stuName` varchar(22) DEFAULT NULL,
  `course` varchar(22) DEFAULT NULL,
  `score` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of grade1
-- ----------------------------
INSERT INTO `grade1` VALUES ('1', '張三', '語文', '91');
INSERT INTO `grade1` VALUES ('2', '張三', '數學', '90');
INSERT INTO `grade1` VALUES ('3', '張三', '英語', '87');
INSERT INTO `grade1` VALUES ('4', '李四', '語文', '79');
INSERT INTO `grade1` VALUES ('5', '李四', '數學', '95');
INSERT INTO `grade1` VALUES ('6', '李四', '英語', '80');
INSERT INTO `grade1` VALUES ('7', '王五', '語文', '77');
INSERT INTO `grade1` VALUES ('8', '王五', '數學', '81');
INSERT INTO `grade1` VALUES ('9', '王五', '英語', '89');

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問題查詢語數外三門課的最低分，還有哪個學生考的
方法一：
SELECT course,SUBSTRING_INDEX((GROUP_CONCAT(stuName ORDER BY score ASC)),',',1) as studentName,MIN(score) from grade1 GROUP BY course;

SELECT
    course,
    SUBSTRING_INDEX(
        (
            GROUP_CONCAT(stuName ORDER BY score ASC)
        ),
        ',',
        1
    ) AS studentName,
    MIN(score)
FROM
    grade1
GROUP BY
    course;

解析：

根據課程course 分組（group by）,min() 函數求該course 下的最低分
group_concat() 函數根據分數從高到底拼接 stuName
substring_index() 函數拆分出分數最低 stuName

數據量大的情況不推薦使用該方法

方法二：
SELECT a.course,a.stuName,a.score from grade1 a where (a.score,a.course) in (SELECT MIN(score),course from grade1 GROUP BY course);

SELECT
    a.course,
    a.stuName,
    a.score
FROM
    grade1 a
WHERE
    (a.score, a.course) IN (
        SELECT
            MIN(score),
            course
        FROM
            grade1
        GROUP BY
            course
    );