mysql JSON_ARRAYAGG 或 GROUP_CONCAT 有限制

Question

在 mysql8.0 中有没有办法在JSON_ARRAYAGG或GROUP_CONCAT内做一个限制？ 例如：

WITH season AS (
    select 'DAL'  as team, 4 as wins, 2000 as season UNION
    select 'DAL'  as team, 10 as wins, 2001 as season UNION
    select 'DAL'  as team, 9 as wins, 2002 as season UNION
    select 'GB'  as team, 2 as wins, 2000 as season UNION
    select 'GB'  as team, 3 as wins, 2001 as season UNION
    select 'GB'  as team, 4 as wins, 2002 as season
) SELECT
    team,
    GROUP_CONCAT(wins order by season desc separator '+') wins_str,
    JSON_ARRAYAGG(wins) wins_arr
FROM season
GROUP BY team;

例如，我如何只获得上述两个领域的前 5 wins ？ 例如，我希望做一些你可以在 BigQuery STRING_AGG做的事情，它接受一个LIMIT 。

Answer 1

最简单的方法是窗口函数：

SELET team,
      GROUP_CONCAT(wins order by season desc separator '+') wins,
      JSON_ARRAYAGG(wins)
from (select s.*,
             row_number() over (partition by team order by seasons desc) as seqnum
      from seasons s
     ) s
where seqnum <= 5
group by team