postgresql - Change single row to multiple rows

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.