PostgreSQL：让 STRING_AGG 遵守 CTE 的顺序

Question

我正在创建一个报告，显示工作人员的前团队以及他们离开的日期，汇总到报告中的一个字段中。这在一定程度上起作用：

WITH "most_recent_leave_dates" AS (
    SELECT
        staff_id, -- alphanumeric string
        team,
        MAX(date_left) AS "most_recent_date_left"
    FROM team_membership
    WHERE date_left IS NOT NULL
    GROUP BY staff_id, team
    -- I thought ordering this CTE would do it, but no
    ORDER BY staff_id, most_recent_date_left DESC
)
SELECT
    staff_id,
    STRING_AGG(
        DISTINCT CONCAT(team, ' until ' || most_recent_date_left),
        CHR(10) -- separate by newline
    ) AS "teams"
FROM most_recent_leave_dates
GROUP BY staff_id

https://www.db-fiddle.com/f/jZCcKRWNV8vLJUFsa6kq7/2

但是 STRING_AGG 正在按字母顺序对术语进行排序。我希望它们按 most_recent_date_left 排序。我该怎么做？

documentation 状态：

Alternatively, supplying the input values from a sorted subquery will usually work.

我是否必须将 CTE 重写为子查询...？

Answer 1

ORDER BY 在 CTE 中没有意义。您可以 ORDER BY 作为 STRING_AGG() 的一部分：

SELECT staff_id,
       STRING_AGG(CONCAT(team, ' until ' || most_recent_date_left),
                  CHR(10)
                  ORDER BY most_recent_date_left DESC
                 ) AS "teams"
FROM most_recent_leave_dates
GROUP BY staff_id;

Answer 2

只需删除 distinct from outer query 如下（我认为您不需要这个）。您的数据已在 cte 中按 staffid 和 most_recent_date_left.

排序

模式（PostgreSQL v9.6）

CREATE TABLE "team_membership" (
  staff_id text,
  team text,
  date_left date
);


INSERT INTO team_membership VALUES
('aaaa', 'B team', '2019-01-01'),
('aaaa', 'A team', '2021-01-01'),
('aaaa', 'C team', '2020-01-01'),
('aaaa', 'A team', '2018-01-01');

查询#1

WITH "most_recent_leave_dates" AS (
    SELECT
        staff_id, 
        team,
        MAX(date_left) AS "most_recent_date_left"
    FROM team_membership
    WHERE date_left IS NOT NULL
    GROUP BY staff_id, team              
)
SELECT
    staff_id,
    STRING_AGG(
         CONCAT(team, ' until ' || most_recent_date_left),
        CHR(10) order by most_recent_date_left  desc
    ) AS "teams"
FROM most_recent_leave_dates
GROUP BY staff_id;

staff_id	teams
aaaa	A team until 2021-01-01 C team until 2020-01-01 B team until 2019-01-01

View on DB Fiddle

PostgreSQL：让 STRING_AGG 遵守 CTE 的顺序

PostgreSQL: Getting STRING_AGG to respect the ordering from a CTE

sql

postgresql

string-agg