mysql - 在单个查询中垂直堆叠 MySQL 结果

Question

我如何将以下 3 个查询合并(垂直堆叠)到 一个查询 中，该查询返回 100 行，50 行来自类别 1，25 行来自类别 2，25 行来自类别 3，所有这些都是随机选择的。我尝试了 UNION 但似乎没有用。

select * from table where category_id = 1 order by rand() limit 50;

select * from table where category_id = 2 order by rand() limit 25;

select * from table where category_id = 3 order by rand() limit 25;

Answer 1

要将 ORDER BY 或 LIMIT 应用于单个 SELECT，请将子句放在包含 SELECT :

(select * from table where category_id = 1 order by rand() limit 50)
UNION ALL
(select * from table where category_id = 2 order by rand() limit 25)
UNION ALL
(select * from table where category_id = 3 order by rand() limit 25);