MySQL get count of periods where date in row - mysql

Question

I have an MySQL table, similar to this example:
c_id date value
66 2015-07-01 1
66 2015-07-02 777
66 2015-08-01 33
66 2015-08-20 200
66 2015-08-21 11
66 2015-09-14 202
66 2015-09-15 204
66 2015-09-16 23
66 2015-09-17 0
66 2015-09-18 231
What I need to get is count of periods where dates are in row. I don't have fixed start or end date, there can be any.
For example: 2015-07-01 - 2015-07-02 is one priod, 2015-08-01 is second period, 2015-08-20 - 2015-08-21 is third period and 2015-09-14 - 2015-09-18 as fourth period. So in this example there is four periods.
SELECT
SUM(value) as value_sum,
... as period_count
FROM my_table
WHERE cid = 66
Cant figure this out all day long.. Thx.

Answer 1

I don't have enough reputation to comment to the above answer.
If all you need is the NUMBER of splits, then you can simply reword your question: "How many entries have a date D, such that the date D - 1 DAY does not have an entry?"
In which case, this is all you need:
SELECT
COUNT(*) as PeriodCount
FROM
`periods`
WHERE
DATE_ADD(`date`, INTERVAL - 1 DAY) NOT IN (SELECT `date` from `periods`);
In your PHP, just select the "PeriodCount" column from the first row.
You had me working on some crazy stored procedure approach until that clarification :P

Answer 2

I should get deservedly flamed for this, but anyway, consider the following...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(date DATE NOT NULL PRIMARY KEY
,value INT NOT NULL
);
INSERT INTO my_table VALUES
('2015-07-01',1),
('2015-07-02',777),
('2015-08-01',33),
('2015-08-20',200),
('2015-08-21',11),
('2015-09-14',202),
('2015-09-15',204),
('2015-09-16',23),
('2015-09-17',0),
('2015-09-18',231);
SELECT x.*
, SUM(y.value) total
FROM
( SELECT a.date start
, MIN(c.date) end
FROM my_table a
LEFT
JOIN my_table b
ON b.date = a.date - INTERVAL 1 DAY
LEFT
JOIN my_table c
ON c.date >= a.date
LEFT
JOIN my_table d
ON d.date = c.date + INTERVAL 1 DAY
WHERE b.date IS NULL
AND c.date IS NOT NULL
AND d.date IS NULL
GROUP
BY a.date
) x
JOIN my_table y
ON y.date BETWEEN x.start AND x.end
GROUP
BY x.start;
+------------+------------+-------+
| start | end | total |
+------------+------------+-------+
| 2015-07-01 | 2015-07-02 | 778 |
| 2015-08-01 | 2015-08-01 | 33 |
| 2015-08-20 | 2015-08-21 | 211 |
| 2015-09-14 | 2015-09-18 | 660 |
+------------+------------+-------+
4 rows in set (0.00 sec) -- <-- This is the number of periods

Answer 3

there is a simpler way of doing this, see here SQLfiddle:
SELECT min(date) start,max(date) end,sum(value) total FROM
(SELECT #i:=#i+1 i,
ROUND(Unix_timestamp(date)/(24*60*60))-#i diff,
date,value
FROM tbl, (SELECT #i:=0)n WHERE c_id=66 ORDER BY date) t
GROUP BY diff
This select groups over the same difference between sequential number and date value.
Edit
As Strawberry remarked quite rightly, there was a flaw in my apporach, when a period spans a month change or indeed a change into the next year. The unix_timestamp() function can cure this though: It returns the seconds since 1970-1-1, so by dividing this number by 24*60*60 you get the days since that particular date. The rest is simple ...
If you only need the count, as your last comment stated, you can do it even simpler:
SELECT count(distinct diff) period_count FROM
(SELECT #i:=#i+1 i,
ROUND(Unix_timestamp(date)/(24*60*60))-#i diff,
date,value
FROM tbl,(SELECT #i:=0)n WHERE c_id=66 ORDER BY date) t

Answer 4

Tnx. #cars10 solution worked in MySQL, but could not manage to get period count to echo in PHP. It returned 0. Got it working tnx to #jarkinstall. So my final select looks something like this:
SELECT
sum(coalesce(count_tmp,coalesce(count_reserved,0))) as sum
,(SELECT COUNT(*) FROM my_table WHERE cid='.$cid.' AND DATE_ADD(date, INTERVAL - 1 DAY) NOT IN (SELECT date from my_table WHERE cid='.$cid.' AND coalesce(count_tmp,coalesce(count_reserved,0))>0)) as periods
,count(*) as count
,(min(date)) as min_date
,(max(date)) as max_date
FROM my_table WHERE cid=66
AND coalesce(count_tmp,coalesce(count_reserved,0))>0
ORDER BY date;