[英]How to RANDOM() select the first/least/… row per group in SQL?
我有一個樣本數據:
id|category_id|name
--------------
1|1|test 1
2|1|test 2
3|1|test 3
4|2|test 4
5|2|test 5
6|2|test 6
和mysql
SELECT p.id, p.name, p.category_id
FROM `test` AS p
WHERE (SELECT count(*) FROM `test` f WHERE f.category_id = p.category_id AND f.id <= p.id) <= 2
ORDER BY RAND()
結果是:
1|1|test 1
2|1|test 2
4|2|test 4
5|2|test 5
=>但是結果不能RANDOM()值獲取其他值(id = 3和id = 6),如何解決?
試試這個..把RAND放在where子句中而不是在ORDER BY中...
從
test
AS中選擇SELECT p.id,p.name,p.category_id p在哪里(從test
f中選擇count(*)從哪里f.category_id = p.category_id和f.id <= p.id)<= 2 AND RAND( )<= 6
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