How to aggregate values from different rows in sql (HANA)? - sql

Question

I have a table of shipments defined like so (the table is stored in a HANA database, if relevant):
CREATE COLUMN TABLE SHIPMENTS (
ShipmentID INT PRIMARY KEY,
Received INT,
Facility NVARCHAR(10),
Item NVARCHAR(20)
);
Here, the 'Received' column denotes the point in time at which each shipment is received, Facility is where the shipment is received and Item is the content of the shipment.
I have filled it with data like so:
INSERT INTO SHIPMENTS VALUES (1, 0, 'Factory', 'Production machine');
INSERT INTO SHIPMENTS VALUES (2, 0, 'Office', 'Printer');
INSERT INTO SHIPMENTS VALUES (3, 0, 'Factory', 'Coffee maker');
INSERT INTO SHIPMENTS VALUES (4, 1, 'Office', 'Coffee maker');
INSERT INTO SHIPMENTS VALUES (5, 1, 'Factory', 'Fax Machine');
INSERT INTO SHIPMENTS VALUES (6, 2, 'Office', 'Computers');
INSERT INTO SHIPMENTS VALUES (7, 2, 'Factory', 'Fridge');
INSERT INTO SHIPMENTS VALUES (8, 2, 'Factory', 'Freezer');
INSERT INTO SHIPMENTS VALUES (9, 2, 'Office', 'Fax Machine');
I would like to query the database to find, at each point in time, which items have been received up until that point. Based on an answer from another thread, I start by doing this:
SELECT Facility, Received, STRING_AGG (Item, ';') as Items
FROM (
SELECT * FROM SHIPMENTS
ORDER BY Facility, Received
)
GROUP BY Facility, Received
ORDER BY Facility, Received;
which results in
| FACILITY | RECEIVED | ITEMS
---------------------------------------------------------
1 | Factory | 0 | Production Machine;Coffee maker
2 | Factory | 1 | Fax Machine
3 | Factory | 2 | Fridge;Freezer
4 | Office | 0 | Printer
5 | Office | 1 | Coffee maker
6 | Office | 2 | Computers;Fax Machine
However, I would like this
| FACILITY | RECEIVED | ITEMS
---------------------------------------------------------
1 | Factory | 0 | Production Machine;Coffee maker
2 | Factory | 1 | Production Machine;Coffee maker;Fax Machine
3 | Factory | 2 | Production Machine;Coffee maker;Fax Machine;Fridge;Freezer
4 | Office | 0 | Printer
5 | Office | 1 | Printer;Coffee maker
6 | Office | 2 | Printer;Coffee maker;Computers;Fax Machine
I.e, each row displays what is received at that point, and everything that has already been received. Is there a nice way to do this in SQL?

Answer 1

You can try using a correlated query in the select clause to generate the csv data you want:
SELECT
Facility,
Received,
(SELECT STRING_AGG (s2.Item, ';') FROM SHIPMENTS s2
WHERE s2.Facility = s1.Facility AND s2.Received <= s1.Received
GROUP BY s2.Facility) AS ITEMS
FROM SHIPMENTS s1
GROUP BY
Facility,
Received
ORDER BY
Facility;

Answer 2

Maybe it could be a good idea to use ORDER BY clause with String_Agg function to make sure that the concatenation will be in desired order
select
distinct Facility, Received,
(
select string_agg(s.Item, ';' order by Received, ShipmentID)
from Shipments s
where
s.Facility = t.Facility and
s.Received <= t.Received
) as Items
from Shipments t