Group by column. If null, group by other column MySQL - mysql

Question

I have this query:
SELECT
vcl.id,
vcl.batch_id,
vcl.type,
vcl.amount,
vcl.date
FROM vrcorporateledger vcl
LEFT JOIN payroll_list pl ON pl.id = vcl.batch_id
which gives the following output:
Whenever there is "CREDIT" in col type I want to increase the running balance by the value in col amount; whenever there is "DEBIT" in col type I want to decrease the accumulated balance by the value in col amount after grouping by batch_id col. So expected result is:
1000-2+5-4-49=950.
If possible I want to also create a column "balance" where at each point/step I see the resulting balance.
expected output like:

Answer 1

WITH cte AS (
SELECT type,
SUM(amount) OVER (PARTITION BY CASE type WHEN 'CREDIT' THEN RAND()
WHEN 'DEBIT' THEN batchID
ELSE 0 END ) amount,
MIN(`date`) OVER (PARTITION BY CASE type WHEN 'CREDIT' THEN RAND()
WHEN 'DEBIT' THEN batchID
ELSE 0 END ) `date`,
SUM(CASE type WHEN 'CREDIT' THEN amount
WHEN 'DEBIT' THEN -amount
ELSE 0 END) OVER (ORDER BY `date`) balance,
batchID,
LEAD(batchID) OVER (ORDER BY `date`) next_batchID
FROM source_data
)
SELECT type,
amount,
balance,
`date`
FROM cte
WHERE CASE WHEN batchID = next_batchID THEN 0 ELSE 1 END
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=75255728f6d64a91a2ebf62edc2d0a0b

Answer 2

I think you're looking for SQL Window functions. They basically allow you to do an aggregate "over a partition".
On a side note: This is a really bad way of calculating doing running balance.
I would strongly suggest storing balance in a separate column at runtime. This should allow you to:
have a strict check even when rows are changed or deleted
normal speed when you have millions of records

Answer 3

If your MySQL version is 8 or above then you can use common table expression with window function as below:
Schema (MySQL v8.0)
create table vrcorporateledger (id int,batch_id int,type varchar(10),amount float,Tdate timestamp);
insert into vrcorporateledger values (1,null,'CREDIT',1000,'2021/03/04 06:19:00');
insert into vrcorporateledger values (2,1,'DEBIT',1,'2021/03/04 07:00:19');
insert into vrcorporateledger values (3,1,'DEBIT',1,'2021/03/04 07:00:25');
insert into vrcorporateledger values (4,null,'CREDIT',5,'2021/03/05 06:19:00');
insert into vrcorporateledger values (5,2,'DEBIT',1,'2021/03/04 08:58:10');
insert into vrcorporateledger values (6,2,'DEBIT',3,'2021/03/04 08:58:16');
insert into vrcorporateledger values (7,null,'DEBIT',49,'2021/03/04 16:42:33');
Query #1
WITH cte AS (
SELECT id,type,
(case when batch_id is null then (case when type='DEBIT' then -amount else amount end) else
SUM(case when type='DEBIT' then -amount else amount end) OVER (PARTITION BY batch_id)end) amount,
(case when batch_id is null then Tdate else
MIN(Tdate) OVER (PARTITION BY batch_id ) end) Trandate,
batch_id,
LEAD(batch_id) OVER (ORDER BY id) next_batch
FROM vrcorporateledger
)
SELECT type,
amount,
sum(amount)over(order by id) running_balance,
Trandate date
FROM cte
WHERE batch_id is null or batch_id =next_batch
order by id;
type
amount
date
running_balance
CREDIT
1000
2021-03-04 06:19:00
1000
DEBIT
-2
2021-03-04 07:00:19
998
CREDIT
5
2021-03-05 06:19:00
1003
DEBIT
-4
2021-03-04 08:58:10
999
DEBIT
-49
2021-03-04 16:42:33
950
View on DB Fiddle