Mysql 选择行并限制不同列

Question

表的结构如下

Posts (
   id int, 
   category_id int, 
   popularity int, 
)

我想选择 5 个类别，每个类别有 5 行。

Like Select * from posts where Category_id in ("1", "2", "3", "4", "5") limit 5 -- 通过选择 5 来限制每个 Category_id

Answer 1

使用 UNION 连接多个 select 语句以显示一个组合结果。
这可能是解决您的问题的最简单方法。

像这样:

SELECT * FROM posts where category_id=1 limit 5
UNION 
SELECT * FROM posts where category_id=2 limit 5
UNION 
SELECT * FROM posts where category_id=3 limit 5
UNION 
SELECT * FROM posts where category_id=4 limit 5
UNION 
SELECT * FROM posts where category_id=5 limit 5

同样的问题已经被问过: MySQL: Limiting number of results received based on a column value | Combining queries 它提供了更复杂的解决方案。