MySQL: count unique days in period with overlaps and gaps (optimized) - mysql

Question

How to calculate the number of unique days per month from a table with two date columns, in which the periods can have gaps and overlaps?
I rather not use a calendar table to get the unique days, because it generates a temporary table with thousands of records, and resources are limited.
Example table:
+---------+------------+------------+
| mygroup | alpha | omega |
+---------+------------+------------+
| 1 | 2017-02-04 | 2017-04-14 |
| 1 | 2017-03-25 | 2017-03-28 |
| 1 | 2017-01-23 | 2017-01-25 |
| 2 | 2017-02-05 | 2017-02-20 |
| 1 | 2017-04-28 | 2017-05-12 |
| etc. | etc. | etc. |
+---------+------------+------------+

Answer 1

Is it what you need?
select count(distinct selected_date),te.mygroup, MONTHNAME(selected_date)from
(select adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) selected_date from
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) v
cross join test te
where selected_date between te.alpha and te.omega
group by mygroup, MONTHNAME(selected_date)
Оutput for your example:
'17','1','April'
'25','1','February'
'3','1','January'
'31','1','March'
'12','1','May'
'16','2','February'
Count may be greater than number of the days in month because such overlap exists in few rows - it's not а mistake.

Answer 2

There is another way to do this roughly 10 times faster than a calendar table.
The biggest resource spoiler is the calendar table itself, it is used to filter unique days.
But instead of using a whole table record for that, it can be done using 31 bits in an UINT.
Recepe:
Create a calendar table with months only
Cut periods in months, and join them with the calendar table
Translate periods to bits of UINTs
OR the UINTs per month for uniqueness
Count their bits as unique days per month
Output:
+--------------+---------+---------+-------+
| Period | Group 1 | Group 2 | Total |
+--------------+---------+---------+-------+
| 2017 month 5 | 11 | 0 | 11 |
| 2017 month 4 | 15 | 0 | 15 |
| 2017 month 3 | 30 | 0 | 30 |
| 2017 month 2 | 24 | 15 | 39 |
| 2017 month 1 | 2 | 0 | 2 |
+--------------+---------+---------+-------+
MySQL query:
SELECT
`tabulate`.`period` AS `Period`,
SUM(IF(`tabulate`.`mygroup` = 1,
`tabulate`.`days`, 0)) AS `Group 1`,
SUM(IF(`tabulate`.`mygroup` = 2,
`tabulate`.`days`, 0)) AS `Group 2`,
SUM(`tabulate`.`days`) AS `Total`
FROM
( SELECT
`unique`.`period`,
BIT_COUNT(BIT_OR(CONV(CONCAT(
REPEAT("1", DAYOFMONTH(`unique`.`omega`) - DAYOFMONTH(`unique`.`alpha`)),
REPEAT("0", DAYOFMONTH(`unique`.`alpha`) - 1)
), 2, 10))) AS `days`,
`unique`.`mygroup`
FROM
( SELECT
DATE_FORMAT(`permonth`.`period_alpha`, "%Y month %c") AS `period`,
GREATEST(`permonth`.`period_alpha`, `permonth`.`example_alpha`) AS `alpha`,
LEAST(`permonth`.`period_omega`, `permonth`.`example_omega`) AS `omega`,
`permonth`.`mygroup`
FROM
( SELECT
`period`.`alpha` AS `period_alpha`,
DATE_SUB(`period`.`omega`, INTERVAL 1 DAY) AS `period_omega`,
`example`.`mygroup`,
IFNULL(`example`.`alpha`, `period`.`alpha`) AS `example_alpha`,
IFNULL(`example`.`omega`, CURDATE()) AS `example_omega`
FROM
( SELECT
DATE_ADD(
MAKEDATE(YEAR(CURDATE()), 1),
INTERVAL `season`.`n` + (`month`.`n` << 2) MONTH
) AS `alpha`,
DATE_ADD(
MAKEDATE(YEAR(CURDATE()), 1),
INTERVAL 1 + `season`.`n` + (`month`.`n` << 2) MONTH
) AS `omega`
FROM
( SELECT 0 AS `n`
UNION ALL SELECT 1
UNION ALL SELECT 2
) AS `month`
CROSS JOIN (SELECT 0 AS `n`
UNION ALL SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 3
) AS `season`
) AS `period`
INNER JOIN
( SELECT 1 AS `mygroup`, "2017-02-04" AS `alpha`, "2017-04-14" AS `omega`
UNION ALL SELECT 1, "2017-03-25", "2017-03-28"
UNION ALL SELECT 1, "2017-01-23", "2017-01-25"
UNION ALL SELECT 2, "2017-02-05", "2017-02-20"
UNION ALL SELECT 1, "2017-04-28", "2017-05-12"
) AS `example` ON (
(`example`.`alpha` < `period`.`omega` OR `example`.`alpha` IS NULL)
AND IFNULL(`example`.`omega`, CURDATE()) >= `period`.`alpha`
)
) AS `permonth`
) AS `unique`
GROUP BY
`unique`.`period`,
`unique`.`mygroup`
) AS `tabulate`
GROUP BY `tabulate`.`period`
ORDER BY `tabulate`.`period` DESC