year month user num
2021 01 anna 1000
2021 01 lily 789
假设有这样一张表，我想要比较同年同月不同user的num值大小并算出差值，sql要怎么写，求教各位大神
select year,month,max(num)-min(num) as cz from tabname group by year,month
——————————————————
SELECT
A.year,
A.month,
A.user,
B.user,
A.num - B.num AS num,
case
when A.num > B.num THEN A.user
WHEN A.num < B.num THEN B.user
ELSE '一样大'
END AS result
FROM
table AS A
INNER JOIN table AS B ON A.year = B.year
AND A.month = B.month
AND A.user <> B.user
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