Select right percentile from joined table - mysql

Question

How to select right value from joined table based on the value in more than one column.
I started sqlfiddle: http://sqlfiddle.com/#!9/f92daa/2
Main table:
id val
1 1
2 4
3 67
4 78
5 22
Joined table:
obs_id perc1 perc2 perc3 perc4 perc5 perc6 perc7 perc8 perc9 perc10
1 1 2 3 4 5 6 7 8 9 10
2 1 2 3 4 5 6 7 8 9 10
3 10 20 30 40 50 60 70 80 90 100
4 10 20 30 40 50 60 70 80 90 100
5 10 20 30 40 50 60 70 80 90 100
Expected result should be:
id val perc
1 1 1
2 4 4
3 67 70
4 78 80
5 22 30
perc - should be number from perc table (joined by ids) not greater than highest possible value form columns perc1-10
Table perc stores percentiles of observations. The goal is to find which interval hit the value from main table and take the upper band.

Answer 1

You can use a case expression to do this. This assumes perc1 < perc2 < perc3 < perc4 < ... and so on.
SELECT obs.id, obs.val,
case when val <= perc1 then perc1
when val <= perc2 then perc2
when val <= perc3 then perc3
when val <= perc4 then perc4
when val <= perc5 then perc5
when val <= perc6 then perc6
when val <= perc7 then perc7
when val <= perc8 then perc8
when val <= perc9 then perc9
when val <= perc10 then perc10
end
perc
FROM obs
INNER JOIN perc
ON obs.id = perc.obs_id
SQL Fiddle

Answer 2

If you are sure that perc table will have always the values in ascending order then
select
a.id, a.val,
case
when b.perc1 >= a.val then b.perc1
when b.perc2 >= a.val then b.perc2
when b.perc3 >= a.val then b.perc3
when b.perc4 >= a.val then b.perc4
when b.perc5 >= a.val then b.perc5
when b.perc6 >= a.val then b.perc6
when b.perc7 >= a.val then b.perc7
when b.perc8 >= a.val then b.perc8
when b.perc9 >= a.val then b.perc9
when b.perc10 >= a.val then b.perc10
end as perc
from idval a , perc b
where a.id = b.obs_id