Sql 每个字段的限制

假设我们有这样一个sql查询，其中包含来自另一个表的连接数据

SELECT 
    pr.num, pr.resort_id, p.src_mask
FROM 
    rutraveler.rt_photo_resort AS pr
    JOIN rutraveler.rt_photo AS p ON pr.photo_id = p.id
WHERE   pr.resort_id = '612' AND p.src_mask is not null
ORDER BY num
LIMIT 30

到目前为止，我们必须对几个度假村id进行几次查询。 如何更改查询，使我们只有一个查询，其中resort\u id位于612、333、111中，每个resort\u id的结果不超过30个项目？

使用ROW\u NUMBER统计每个resort\u id的行数

您可以使用带有行号和分区的CTE

---

如果没有分区排序，结果是错误的。

SELECT resort_id, num, resort_id, src_mask 
FROM
(
  SELECT 
    pr.resort_id, pr.num, pr.resort_id, p.src_mask,
    ROW_NUMBER() OVER (PARTITION BY pr.resort_id ORDER BY num) AS rn
  FROM 
    rutraveler.rt_photo_resort AS pr
    JOIN rutraveler.rt_photo AS p ON pr.photo_id = p.id
  WHERE resort_id in (612, 333, 111) AND p.src_mask is not null
) data
WHERE rn <= 30
ORDER BY resort_id, num;

WITH Results_CTE AS
(
    SELECT 
    pr.num, pr.resort_id, p.src_mask,ROW_NUMBER() over ( PARTITION BY pr.resort_id ORDER BY num) As Row_number
FROM 
    rutraveler.rt_photo_resort AS pr
    JOIN rutraveler.rt_photo AS p ON pr.photo_id = p.id
WHERE   pr.resort_id IN (A,B,C) AND p.src_mask is not null   
)

SELECT *
FROM Results_CTE
WHERE Row_number <= 30