sql - 每个字段的限制

Question

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 resort_id 进行多次查询。
如何更改查询，以便我们只有一个查询(WHERE resort_id in (612, 333, 111)，每个 resort_id 结果不超过 30 项？

Answer 1

使用 ROW_NUMBER 计算每个 resort_id 的行数。

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;