get total amount of expenses per month in MySQL - mysql

Question

I am currently working with 2 tables, expenses and income. To keep the structure simple and can see it, this is the fiddle: http://sqlfiddle.com/#!9/256cd64/2
The result I need from my query is the total amount for each month of the current year, for this and tried something like this:
select sum(e.amount) as expense, DATE_FORMAT(e.date,'%m') as month
from expenses e
where year(e.date) = 2019
group by month
My problem with this is that it only takes me the months where there was registration and I would like it to take 12 months whether or not they have a registration, in the case that they did not return 0 as a total amount.
At the moment I am working with the table of expenses but I would like to have a single query that returns the monthly expenses and income, this is an example of the final output that I would like to obtain:
| Month | Expense| Incomes |
|---------|--------|---------|
| 01| 0 | 0 |
| 02| 3000 | 4000 |
| 03| 1500 | 5430 |
| 04| 2430 | 2000 |
| 05| 2430 | 1000 |
| 06| 2430 | 1340 |
| 07| 0 | 5500 |
| 08| 2430 | 2000 |
| 09| 1230 | 2000 |
| 10| 8730 | 2000 |
| 11| 2430 | 2000 |
| 12| 6540 | 2000 |

Answer 1

You need to generate the month values and then use left join to match to expenses:
select coalesce(sum(e.amount), 0) as expense, m.month
from (select '01' as month union all
select '02' as month union all
select '03' as month union all
select '04' as month union all
select '05' as month union all
select '06' as month union all
select '07' as month union all
select '08' as month union all
select '09' as month union all
select '10' as month union all
select '11' as month union all
select '12' as month
) m left join
expenses e
on year(e.date) = 2019 and
DATE_FORMAT(e.date,'%m') = m.month
group by m.month;
Here is a db<>fiddle.
As for income, you should ask another question about that.

Answer 2

You can use MONTH to get month value from your date column and then GROUP BY them to get your desired output as below-
SELECT SUM(e.amount) AS expense,
MONTH(e.date) AS month
FROM expenses e
WHERE YEAR(e.date) = 2019
GROUP BY MONTH(e.date)

Answer 3

Try changing your sum(e.amount) as expense to: COALESCE(sum(e.amount),0) as expense
The COALESCE function returns the first non NULL value.

Answer 4

SELECT
t1.month,
COALESCE(t2.amount, 0) AS expenses,
COALESCE(t3.amount, 0) AS incomes
FROM
(
SELECT 1 AS month UNION ALL
SELECT 2 UNION ALL
SELECT 3 UNION ALL
SELECT 4 UNION ALL
SELECT 5 UNION ALL
SELECT 6 UNION ALL
SELECT 7 UNION ALL
SELECT 8 UNION ALL
SELECT 9 UNION ALL
SELECT 10 UNION ALL
SELECT 11 UNION ALL
SELECT 12
) t1
LEFT JOIN
(
SELECT MONTH(date) AS month, SUM(amount) AS amount
FROM expenses
GROUP BY MONTH(date)
) t2
ON t1.month = t2.month
LEFT JOIN
(
SELECT MONTH(date) AS month, SUM(amount) AS amount
FROM incomes
GROUP BY MONTH(date)
) t3
ON t1.month = t3.month
ORDER BY
t1.month;