mysql - GROUP BY grouping multiple values as the same group -

i have table similar this:

id      week 1       1 2       1 3       1 4       2 5       2 6       3 7       3 8       3 

this current query:

select count(*), `week` data group `week` 

here's sqlfiddle http://sqlfiddle.com/#!2/bfdb6/2/0

what need group rows every 2 weeks same count.

so instead of this:

count(*)    week 3           1 2           2 3           3 3           4 

i'd get:

count(*)    week 5           1 5           2 6           3 3           4 

where every week has next weeks count added it.

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question amended:

i should have been clear needed.

rather grouping weeks 1 , 3, need grouping every 2 weeks.

so group weeks 1 , 2, 2 , 3, 3 , 4, 4 , 5, etc

automatically if possible, sql generated outside query week groupings.

thanks.

i think have you...

first, distinct weeks available data... then, join data on either week or week +1

i applied existing sqlfiddle , appeared work.

select       justweeks.`week`,       count(*) twoweeksum          ( select distinct               `week`                          data ) justweeks       join data           on justweeks.`week` = data.`week`          or justweeks.`week` +1 = data.`week`    group       justweeks.`week`