MySQL没有PIVOT功能
SELECT userid,
MAX(CASE WHEN `type` = 1 THEN itemcount END) AS type_1,
MAX(CASE WHEN `type` = 2 THEN itemcount END) AS type_2,
MAX(CASE WHEN `type` = 3 THEN itemcount END) AS type_3,
MAX(CASE WHEN `type` = 4 THEN itemcount END) AS type_4
FROM count_paper_1
GROUP BY userid
ORDER BY userid DESC
http://www.cppcns.com/shujuku/mysql/267968.html
https://www.jianshu.com/p/7befd2eb5e88
https://www.5axxw.com/questions/content/rjvex8