[PostgreSQL]在group by查询下拼接列字符串

首先创建group_concat聚集函数:

CREATE AGGREGATE group_concat(anyelement)
(
sfunc = array_append, -- 每行的操作函数，将本行append到数组里
stype = anyarray, -- 聚集后返回数组类型
initcond = '{}' -- 初始化空数组
);

接着上一个SQL样例：
在订单明细表按po和season分组，把ticket_code和order_id去除重复并且拼接起来

--wp_order_detail
SELECT
	po,
	season,
	array_to_string( group_concat ( DISTINCT ticket_code ), ',' ) AS ticket_codes,
	array_to_string( group_concat ( DISTINCT order_id ), ',' ) AS order_ids
FROM
	wp_order_detail
WHERE
	exists (select 1 from wp_order orders where orders.id = order_id and type = 'Po')
GROUP BY
	po,
	season;

最后查询结果截图：