Date period spread among seasons

Question

In my MySQL database table I have the following date periods (seasons):

sstart,send,sname
2013-05-01,2013-05-31,'season1'
2013-06-01,2013-06-30,'season2'

I'd like to create SQL query which will for given start and end date split this period among seasons with info about duration of each part of period:

For example for the following period (qstart,qend) 2013-04-20,2013-06-10 this query should return:

2013-04-20,2013-04-30,'',11           <-- this is important - I need it
2013-05-01,2013-05-31,'season1',31    <-- 31 days of my period is in season1
2013-06-01,2013-06-10,'season2',10    <-- 10 days of my period is in season2

I have the following SQL query:

SELECT sid,sname,DATEDIFF(IF(send>@qend,@qend,send),IF(sstart<@qstart,@qstart,sstart))+1
               FROM seasons WHERE sstart<=@qend AND send>=@qstart

My problem is when my period (qstart,qend) starts before first season or ends after the last season in database, this query does not return these tails which I need.

Answer 1

I don't have mySQL, but this should hopefully point you in the right direction:

Instead of the Seasons table in your query, using the following:

   FROM 
   ( 
     select * from seasons 
     union
     select '' as [sname],'1/1/1980' as [sStart],DateAdd(dd,-1,MIN([sStart])) as [send]
     from Seasons
     union
     select '' as [sname],DateAdd(dd,+1,MAX([send])) as [sstart],'12/31/2021' as [Send]
     from Seasons
    ) Seasons         

Basically, adding two "dummy rows" to represent seasons before the first date and after the last date...

Answer 2

For others, according to Sparky's suggestion here is my query:

SELECT sid,sstart,send,sname,DATEDIFF(IF(send>@lDay,@lDay,send),IF(sstart<@fDay,@fDay,sstart))+1 AS duration
FROM
(
  SELECT 0 AS sid,'undefined' AS sname,'1980-01-01' AS sstart,SUBDATE(MIN(sstart),1) AS send FROM seasons
    UNION
  SELECT sid,sname,sstart,send FROM seasons
    UNION
  SELECT 0 AS sid,'undefined' AS sname,ADDDATE(MAX(send),1) AS sstart,'2021-12-31' AS send FROM seasons
) AS seasons
WHERE sstart<=@lDay AND send>=@fDay
ORDER BY sstart