查询以逗号分隔返回列值 - postgresql

Question

I am using materialized view in my application.

The query is as follows

SELECT
  DISTINCT n.order_id,
  CASE
    WHEN n.customer_billing = TRUE THEN 'AR (Customer Billing)'
    WHEN n.commander = TRUE THEN 'AP (Commander)'
    WHEN n.agent = TRUE THEN 'AP (Agent)'
    ELSE NULL
  END AS finance
FROM
  pt.notes n
 WHERE
 n.order_id = 891090 AND
  (n.customer_billing = TRUE or n.commander = TRUE or n.agent = TRUE)

This produces the following output

Instead of two records, the output of finance column should be comma separated values.

That is the output should be

AP (Agent), AR (Customer Billing)

I know aggregate functions can be used here, but not sure how to use when the query has switch cases and all.

Any idea on how to achieve this?

Answer 1

Consider: Seldom is it wise to de-normalize data this way in the database query; Better done in UI. However, if this is going directly to an aggregated report; it may make sense to do it here... But keep in mind if this ever will need to be separated later; you're better off doing the combine in the UI.

Notes:

• Wrap case in string_Agg() function the "Case" statement is then wrapped in the string_agg() function and since we operate inside out just like math, the case is resolved 1st.
• added GROUP BY for non-aggregated element(s)
• eliminated DISTINCT as GROUP BY takes care of it so distinct is unneeded clutter.
• added additional sample data to show how multiple columns handled.
• eliminated pt.notes table as I'm not using it in my generated common table expression
• You will not need the "with notes as ()..." Just the select after it and correct the FROM clause to yours

dbfiddle.uk Example

More on this--> How to concatenate string of a string field in postgresql

WITH notes AS (
  SELECT 891090 Order_ID, False customer_billing,  false commander, true agent UNION ALL
  SELECT 891090, true, false, false UNION ALL
  SELECT 891091, false, true, false UNION ALL
  SELECT 891091, true, false, false)

SELECT
  n.order_id,
  string_Agg(CASE
    WHEN n.customer_billing = TRUE THEN 'AR (Customer Billing)'
    WHEN n.commander = TRUE THEN 'AP (Commander)'
    WHEN n.agent = TRUE THEN 'AP (Agent)'
    ELSE NULL
  END,', ') AS finance
FROM notes n
 WHERE
 n.order_id = 891090 AND
  (n.customer_billing = TRUE or n.commander = TRUE or n.agent = TRUE)
 GROUP BY ORDER_ID

Giving us:

+----------+---------------------------------------+
| order_id |                finance                |
+----------+---------------------------------------+
|   891091 | AP (Commander), AR (Customer Billing) |
|   891090 | AP (Agent), AR (Customer Billing)     |
+----------+---------------------------------------+