[英]sql get the max 3 score rows for each category
I have a table with data as follows: 我有一个数据表,如下所示:
cat score
a 80
c 88
b 36
b 96
d 99
b 76
d 89
a 50
d 69
b 36
d 59
b 96
b 86
c 98
a 50
a 90
c 83
b 66
How can I use SQL to get the max 3 score rows for each cat? 如何使用SQL获取每只猫的最高3分行?
You can use variables for this: 您可以为此使用变量:
SELECT cat, score
FROM (
SELECT cat, score,
@seq := IF(@c = cat, @seq + 1,
IF(@c := cat, 1, 1)) AS seq
FROM mytable
CROSS JOIN (SELECT @c := '', @seq := 0) x
ORDER BY cat, score DESC ) AS t
WHERE seq <= 3
You can use union 你可以用工会
(select cat, score
from my_table
where cat='a'
order by score desc
limit 3)
union
(select cat, score
from my_table
where cat='b'
order by score desc
limit 3)
union
(select cat, score
from my_table
where cat='c'
order by score desc
limit 3)
union
(select cat, score
from my_table
where cat='d'
order by score desc
limit 3)
You can do it with a correlated query : 您可以使用相关查询来做到这一点:
SELECT tt.cat,tt.score FROM (
SELECT t.cat,t.score,
(SELECT COUNT(*) FROM YourTable s FROM YourTable s
WHERE s.cat = t.cat and t.score <= s.score) as cnt
FROM YourTable t) tt
WHERE tt.cnt < 4
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