2列上的array_agg（）函數

Question

我在下面的桌子

CUST_ID integer          | servername text        | DATE
---------------------    |---------------------------------------
    1                    | '1'                    | '2017-01-15'
    1                    | '1'                    | '2017-02-15'
    2                    | '1'                    | '2017-01-15'
    2                    | '2'                    | '2017-01-15'

我想這樣提取信息。

CUST_ID integer          | servername text        | DATE
-------------------------|------------------------|------------------------------
    1                    | '1'                    | {'2017-01-15', '2017-02-15'}
    2                    | {'1', '2'}             | '2017-01-15'

我已經嘗試了GROUP BY CUST_ID, DATE UNION GROUP BY CUST_ID, SERVICE這樣。 顯然我收到一個ERROR: UNION types text and text[] cannot be matched因為在第一個選擇查詢中， servername不是數組。

SELECT CUST_ID, servername, array_agg(trans_date) FROM infomation
GROUP by CUST_ID, servername

UNION 
SELECT CUST_ID, array_agg(servername), trans_date FROM infomation
GROUP by CUST_ID, trans_date;

Answer 1

select      cust_id
           ,array_agg(distinct servername)      as servername
           ,array_agg(distinct date)            as date

from        information

group by    cust_id

---

+---------+------------+-------------------------+
| cust_id | servername |          date           |
+---------+------------+-------------------------+
|       1 | {"1"}      | {2017-01-15,2017-02-15} |
|       2 | {"1","2"}  | {2017-01-15}            |
+---------+------------+-------------------------+

Answer 2

您將在第二列中混合text和text[]以及在第三列中混合date和date[] 。 那永遠都行不通。 如果您可以在所有情況下使用數組，那么這應該可以工作：

SELECT cust_id,
       array_agg(DISTINCT servername) AS service,
       array_agg(DISTINCT trans_date) AS trans_date
FROM information
GROUP BY cust_id;