MYSQL: Display one query from a select statement from two unrelated tables - mysql

Question

I'm trying to display the sum of monthly revenue from different unrelated tables, Where i display the budgeted against the actual usage
I have two tables Planned Budget and actual budget, with with similar columns but different data, in a query i want retrieve the sum of budget and group it Yearly and monthly.
Planned Budget table
+-----+-------+-------------+-------------+
| uid | codes | opca_budget | date_period |
+-----+-------+-------------+-------------+
| 10 | 3210 | 3000 | 2018-03-01 |
| 17 | 3355 | 3000 | 2018-03-01 |
| 33 | 3210 | 4000 | 2018-04-01 |
| 40 | 3355 | 4000 | 2018-04-01 |
| 56 | 3210 | 5000 | 2018-05-01 |
| 63 | 3355 | 5000 | 2018-05-01 |
| 79 | 3210 | 6000 | 2018-06-01 |
| 86 | 3355 | 6000 | 2018-06-01 |
| 109 | 3355 | 45000 | 2018-07-01 |
Actual Budget
+-----+-------+-------------+---------------------+
| uid | codes | opca_budget | date_period |
+-----+-------+-------------+---------------------+
| 10 | 3210 | 6500 | 2018-03-01 00:00:00 |
| 17 | 3355 | 6500 | 2018-03-01 00:00:00 |
| 18 | 3120 | 6500 | 2018-03-01 00:00:00 |
| 33 | 3210 | 7500 | 2018-04-01 00:00:00 |
| 40 | 3355 | 7500 | 2018-04-01 00:00:00 |
| 41 | 3120 | 7500 | 2018-04-01 00:00:00 |
| 56 | 3210 | 8500 | 2018-05-01 00:00:00 |
| 63 | 3355 | 8500 | 2018-05-01 00:00:00 |
| 64 | 3120 | 8500 | 2018-05-01 00:00:00 |
I tried to combine them horizontally, But i get wrong results
SELECT YEAR(c.date_period)
, MONTH(c.date_period)
, SUM(c.opca_budget) MonthlyBudget
, SUM(a.opca_budget) MonthlyUsage
FROM opexcapex c
LEFT
JOIN opxcpx_actuals a
ON YEAR(c.date_period) = YEAR(a.date_period)
AND MONTH(c.date_period) = MONTH(a.date_period)
WHERE c.date_period BETWEEN '2018-03-01' AND '2019-02-29'
GROUP
BY YEAR(c.date_period)
, MONTH(c.date_period);
+------+-------+---------------+--------------+
| Year | Month | MonthlyBudget | MonthlyUsage |
+------+-------+---------------+--------------+
| 2018 | 3 | 168000 | 364000 |
| 2018 | 4 | 224000 | 420000 |
| 2018 | 5 | 280000 | 476000 |
| 2018 | 6 | 336000 | 532000 |
| 2018 | 7 | 2520000 | 588000 |
| 2018 | 8 | 576000 | 367200 |
| 2018 | 9 | 3240000 | 367200 |
| 2018 | 10 | 720000 | 252000 |
| 2018 | 11 | 792000 | 1807200 |
| 2018 | 12 | 2583000 | 1323000 |
| 2019 | 1 | 9000 | NULL |
| 2019 | 2 | 36000 | NULL |
+------+-------+---------------+--------------+
I expect to get results like this:
+-----------+-------------+---------------+--------------+
| BudgtYear | BudgetMonth | MonthlyBudget | MonthlyUsage |
+-----------+-------------+---------------+--------------+
| 2018 | 3 | 24000 | 45500 |
| 2018 | 4 | 32000 | 52500 |
| 2018 | 5 | 40000 | 59500 |
| 2018 | 6 | 48000 | 66500 |
| 2018 | 7 | 360000 | 73500 |
| 2018 | 8 | 72000 | 40800 |
| 2018 | 9 | 405000 | 40800 |
| 2018 | 10 | 90000 | 28000 |
| 2018 | 11 | 99000 | 200800 |
| 2018 | 12 | 369000 | 147000 |
| 2019 | 1 | 9000 | |
| 2019 | 2 | 36000 | |
+-----------+-------------+---------------+--------------+

Answer 1

You want to do a UNION ALL as a sub-query and then calculate the sum on the value from that sub-query, notice also that I use two amount columns in the union but one is always null, this is to have the two selects return the same number of columns but separated values
SELECT YEAR(date_period) as year, MONTH(date_period) as month, SUM(mbudget) AS MonthlyBudget, SUM(musage) as MonthlyUsage
FROM (SELECT date_period, opca_budget mbudget, null musage
FROM opexcapex
UNION ALL
SELECT date_period, null, opca_budget
FROM opxcpx_actuals
) sq
WHERE date_period BETWEEN '2018-03-01' AND '2019-02-29'
GROUP BY year, month

Answer 2

You should be able to UNION the 2 tables first, then SELECT from the resulting data, something like this (Updated query) :-
SELECT YEAR(date_period), MONTH(date_period), MonthlyBudget, MonthlyUsage
FROM
(SELECT date_period, opca_budget as MonthlyBudget, 0 as MonthlyUsage FROM
opexcapex
UNION
SELECT date_period, 0 as MonthlyBudget, opca_budget as MonthlyUsage FROM
opxcpx_actuals) T1
WHERE date_period BETWEEN '2018-03-01' AND '2019-02-29'
GROUP BY YEAR(date_period), MONTH(date_period);