行转列、合并字段、列转行

CREATE TABLE `TEST_TB_GRADE` (
    `ID` int(10) NOT NULL AUTO_INCREMENT,
    `USER_NAME` varchar(20) DEFAULT NULL,
    `COURSE` varchar(20) DEFAULT NULL,
    `SCORE` float DEFAULT '0',
    PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
insert into TEST_TB_GRADE(USER_NAME, COURSE, SCORE) values
("张三", "数学", 34),("张三", "语文", 58),("张三", "英语", 58),
("李四", "数学", 45),("李四", "语文", 87),("李四", "英语", 45),
("王五", "数学", 76),("王五", "语文", 34),("王五", "英语", 89);
insert into test_tb_grade (user_name,course,score) values ("张三","数学",34)

-- 行转列（最大值）

select user_name,
    MAX(CASE WHEN course='数学' THEN score ELSE 0 END) 数学,
    MAX(CASE WHEN course='语文' THEN score ELSE 0 END) 语文,
    MAX(CASE WHEN course='英语' THEN score ELSE 0 END) 英语
    from TEST_TB_GRADE GROUP BY user_name

-- 行转列（合计）

select user_name,
    SUM(CASE WHEN course='数学' THEN score ELSE 0 END) 数学,
    SUM(CASE WHEN course='语文' THEN score ELSE 0 END) 语文,
    SUM(CASE WHEN course='英语' THEN score ELSE 0 END) 英语
    from TEST_TB_GRADE GROUP BY user_name

-- 合并字段

select user_name,GROUP_CONCAT(course,":",score) from TEST_TB_GRADE GROUP BY user_name

CREATE TABLE `TEST_TB_GRADE2` (
    `ID` int(10) NOT NULL AUTO_INCREMENT,
    `USER_NAME` varchar(20) DEFAULT NULL,
    `CN_SCORE` float DEFAULT NULL,
    `MATH_SCORE` float DEFAULT NULL,
    `EN_SCORE` float DEFAULT '0',
    PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
insert into TEST_TB_GRADE2(USER_NAME, CN_SCORE, MATH_SCORE, EN_SCORE) values
("张三", 34, 58, 58),("李四", 45, 87, 45),("王五", 76, 34, 89);

-- 列转行

select user_name, '语文' COURSE , CN_SCORE as SCORE from test_tb_grade2
union select user_name, '数学' COURSE, MATH_SCORE as SCORE from test_tb_grade2
union select user_name, '英语' COURSE, EN_SCORE as SCORE from test_tb_grade2
order by user_name,COURSE;