How to get the MIN and MAX date from each month

Question

I have a data in mysql that look like this in my first table.

ID |     date_created        | cost  |  project_id
1   2019-09-01 00:00:00         10          1
2   2019-09-02 00:00:00         20          1
3   2019-09-03 00:00:00         30          1
4   2019-09-04 00:00:00         40          1
5   2019-09-05 00:00:00         50          1
6   2019-10-01 00:00:00         20          5
7   2019-10-02 00:00:00         40          5
8   2019-10-03 00:00:00         60          5
9   2019-10-04 00:00:00         70          5
10  2019-10-12 00:00:00         80          5

Here is my second table

ID |     date_created        | usage  |  project_id
1   2019-09-01 00:00:00         10          1
2   2019-09-02 00:00:00         20          1
3   2019-09-03 00:00:00         30          1
4   2019-09-04 00:00:00         40          1
5   2019-09-05 00:00:00         50          1
6   2019-10-01 00:00:00         20          5
7   2019-10-02 00:00:00         40          5
8   2019-10-03 00:00:00         60          5
9   2019-10-04 00:00:00         70          5
10  2019-10-12 00:00:00         80          5

the results that i am trying to achieved is like this.

ID | date_created             | cost(SUM) | total_usage (SUM)

1    2019-09-01 - 2019-09-05     150      |  150

2    2019-10-01 - 2019-10-12     260      |  260

this is my query. i can already get the sum of the cost but when i put the the LEFT JOIN to get the sum of the usage, instead of having 2 rows only. im getting wrong values and having multiple rows.

SELECT MONTHNAME(date_created), SUM(cost), SUM(usage)
FROM first_table as first_table
LEFT JOIN second_table as second_table ON first_table.project_id = second_table.project_id
GROUP BY MONTH(first_table.date_created), YEAR(first_table.date_created)

i need help in getting the sum of the cost and also the usage. is there any way to do this, or my way is just wrong.

Answer 1

You should never consider months without also considering the year. Also, the unaggregated columns in the SELECT should match the columns in the GROUP BY . Most databases enforce this, including the most recent versions of MySQL.

The answer to your question is to just include the additional columns you want in the SELECT :

SELECT YEAR(date_created), MONTHNAME(date_created), SUM(cost), MIN(cost), MAX(cost)
FROM table_name
GROUP BY YEAR(date_created), MONTH(date_created), MONTHNAME(date_created);

Answer 2

This should return the results that you expect. It's a simple aggregate query where results are grouped by year and month (grouping on month only would cause issues if your data spans over multiple years):

SELECT 
    CONCAT(MIN(date_created), ' - ', MAX(date_created)) date_interval, 
    SUM(cost) total_cost
FROM mytable
GROUP BY YEAR(date_created), MONTH(date_created)

Demo on DB Fiddle :

| date_interval           | total_cost |
| ----------------------- | ---------- |
| 2019-09-01 - 2019-09-05 | 150        |
| 2019-10-01 - 2019-10-12 | 270        |