MySql 查询通过 rand() 从 limit 和 order 中获取一定数量的值

Question

在下面的 SQL 查询中，我需要 25 行包含产品 = 'y' 和 25 行包含产品 = 'n'。 产品是仅具有 Y/N 值的列。在随机 50 行的限制中，我需要每个值 25 行。

SELECT qno 
FROM `wp_question_bank` 
where brand='XYZ' 
and department='DOMESTIC' 
and product = 'y' 
and priority = 'p1' 
ORDER BY RAND() limit 50

请帮忙。我尝试过联合但没有成功。

Answer 1

只需对每种产品类型使用UNION:

(SELECT qno
FROM `wp_question_bank`
WHERE brand='XYZ' AND department='DOMESTIC' AND product = 'y' AND priority = 'p1'
ORDER BY RAND()
LIMIT 25)

UNION ALL

(SELECT qno
FROM `wp_question_bank`
WHERE brand='XYZ' AND department='DOMESTIC' AND product = 'n' AND priority = 'p1'
ORDER BY RAND()
LIMIT 25)