MySQL数据透视功能
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

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