postgresql - Change single row to multiple rows - sql

Question

I have a table named payment_info, with the following records.
paymentid | customercode | previousbalance | paymentamount | remainingbalance
-----------------------------------------------------------------------------
PID0001 | CUST024 | 10000 | 2500 | 7500
PID0002 | CUST031 | 8500 | 3500 | 5000
PID0003 | CUST005 | 12000 | 1500 | 10500
Then what I want is to create a 3 rows per row of the above table.
I want my results to look like this.
Payment Group | Payment Line Item | Payment ID | Customer Code | Type | Amount
--------------------------------------------------------------------------------------------------
1 | 1 | PID0001 | CUST024 | PREVIOUS BALANCE | 10000.00
1 | 2 | | | PAYMENT AMOUNT | 2500.00
1 | 3 | | | REMAINING BALANCE | 7500.00
2 | 1 | PID0002 | CUST031 | PREVIOUS BALANCE | 8500.00
2 | 2 | | | PAYMENT AMOUNT | 3500.00
2 | 3 | | | REMAINING BALANCE | 5000.00
3 | 1 | PID0003 | CUST005 | PREVIOUS BALANCE | 12000.00
3 | 2 | | | PAYMENT AMOUNT | 1500.00
3 | 3 | | | REMAINING BALANCE | 10500.00
Here is the query I've started. But it did not return results same as above.
select row_number() over() as id,paymentid,customercode,'PREVIOUS BALANCE' as type,previousbalance from payment_info
union
select row_number() over() as id,'','','PAYMENT AMOUNT' as type,paymentamount from payment_info
union
select row_number() over() as id,'','','REMAINING BALANCE' as type,remainingbalance from payment_info
Is there other ways, where I will not use UNION Keyword? Cause in the real table, I will be using 30+ columns, querying thousands of records.
I also don't know how to create auto generated number (id) from payment group (per payment id) and Payment Line Item (per group).
thanks

Answer 1

version with whitespace (empty text)
The unnest function can do this for you.
And if you want the empty text then you can use this
SELECT ROW_NUMBER() OVER (ORDER BY paymentid) AS "group",
unnest(array[1, 2, 3]) AS "line item",
unnest(array[paymentid, '', '']) AS "paymentid",
unnest(array[customercode, '', '']) AS "customercode",
unnest(array['PREVIOUS BALANCE', 'PAYMENT AMOUNT', 'REMAINING BALANCE']) AS "type",
unnest(array[previousbalance, paymentamount, remainingbalance]) AS "amount"
FROM payment_info
ORDER BY 1, 2 ;
To get this
group | line item | paymentid | customercode | type | amount
-------+-----------+-----------+--------------+-------------------+--------
1 | 1 | PID0001 | CUST024 | PREVIOUS BALANCE | 10000
1 | 2 | | | PAYMENT AMOUNT | 2500
1 | 3 | | | REMAINING BALANCE | 7500
2 | 1 | PID0002 | CUST031 | PREVIOUS BALANCE | 8500
2 | 2 | | | PAYMENT AMOUNT | 3500
2 | 3 | | | REMAINING BALANCE | 5000
3 | 1 | PID0003 | CUST005 | PREVIOUS BALANCE | 12000
3 | 2 | | | PAYMENT AMOUNT | 1500
3 | 3 | | | REMAINING BALANCE | 10500
If you want to have, for example points or other text, or arrows in the empty text columns, you can do this easily with unnest.
You can control the 4 empty text values individually.
SELECT ROW_NUMBER() OVER (ORDER BY paymentid) AS "group",
unnest(array[1, 2, 3]) AS "line item",
unnest(array[paymentid, ' a', ' c']) AS "paymentid",
unnest(array[customercode, ' b', ' d']) AS "customercode",
unnest(array['PREVIOUS BALANCE', 'PAYMENT AMOUNT', 'REMAINING BALANCE']) AS "type",
unnest(array[previousbalance, paymentamount, remainingbalance]) AS "amount"
FROM payment_info
ORDER BY 1, 2 ;
to generate
group | line item | paymentid | customercode | type | amount
-------+-----------+-----------+--------------+-------------------+--------
1 | 1 | PID0001 | CUST024 | PREVIOUS BALANCE | 10000
1 | 2 | a | b | PAYMENT AMOUNT | 2500
1 | 3 | c | d | REMAINING BALANCE | 7500
2 | 1 | PID0002 | CUST031 | PREVIOUS BALANCE | 8500
2 | 2 | a | b | PAYMENT AMOUNT | 3500
2 | 3 | c | d | REMAINING BALANCE | 5000
3 | 1 | PID0003 | CUST005 | PREVIOUS BALANCE | 12000
3 | 2 | a | b | PAYMENT AMOUNT | 1500
3 | 3 | c | d | REMAINING BALANCE | 10500
It's a very flexible solution, you know.

Answer 2

It isn't necessary to always use union queries. Here for example you can use 3 rows and a cross join instead. This has the advantage of only a single pass over the source table.
drop table if exists Table1;
CREATE TABLE Table1
("paymentid" varchar(7), "customercode" varchar(7)
, "previousbalance" int, "paymentamount" int, "remainingbalance" int)
;
INSERT INTO Table1
("paymentid", "customercode", "previousbalance", "paymentamount", "remainingbalance")
VALUES
('PID0001', 'CUST024', 10000, 2500, 7500),
('PID0002', 'CUST031', 8500, 3500, 5000),
('PID0003', 'CUST005', 12000, 1500, 10500)
;
select
paymentid
, customercode
, rn
, typeof
, case when rn = 1 then previousbalance
when rn = 2 then paymentamount
when rn = 3 then remainingbalance
end as Amount
from Table1
cross join (select 1 rn , 'previousbalance' typeof
union all
select 2 , 'paymentamount'
union all
select 3, 'remainingbalance'
) rns
That data/query produces this result:
+----+-----------+--------------+----+------------------+--------+
| | paymentid | customercode | rn | typeof | amount |
+----+-----------+--------------+----+------------------+--------+
| 1 | PID0001 | CUST024 | 1 | previousbalance | 10000 |
| 2 | PID0001 | CUST024 | 2 | paymentamount | 2500 |
| 3 | PID0001 | CUST024 | 3 | remainingbalance | 7500 |
| 4 | PID0002 | CUST031 | 1 | previousbalance | 8500 |
| 5 | PID0002 | CUST031 | 2 | paymentamount | 3500 |
| 6 | PID0002 | CUST031 | 3 | remainingbalance | 5000 |
| 7 | PID0003 | CUST005 | 1 | previousbalance | 12000 |
| 8 | PID0003 | CUST005 | 2 | paymentamount | 1500 |
| 9 | PID0003 | CUST005 | 3 | remainingbalance | 10500 |
+----+-----------+--------------+----+------------------+--------+
Please then note that SQL isn't a "report writer" so blanks in columns for "layout" are not a good fit for SQL which wants to repeat information (like you see above in the result) so that you can sort and filter as needed.