这是我参与更文挑战的第 1 天，活动详情查看：更文挑战
未转数据前：
1.使用case...when....then 进行行转列：
SELECT userid,
SUM(CASE `subject` WHEN '语文' THEN score ELSE 0 END) as '语文',
SUM(CASE `subject` WHEN '数学' THEN score ELSE 0 END) as '数学',
SUM(CASE `subject` WHEN '英语' THEN score ELSE 0 END) as '英语',
SUM(CASE `subject` WHEN '政治' THEN score ELSE 0 END) as '政治'
FROM tb_score
GROUP BY userid
2.使用IF() 进行行转列： IF(true=true,true,false)
SELECT userid,
SUM(IF(`subject`='语文',score,0)) as '语文',
SUM(IF(`subject`='数学',score,0)) as '数学',
SUM(IF(`subject`='英语',score,0)) as '英语',
SUM(IF(`subject`='政治',score,0)) as '政治'
FROM tb_score
GROUP BY userid
