Question

Sorry for messy title, if you are a moderator and know a better title, feel free to change.

Say, we have two SQL tables

intervals           vals       
--------            -------    
since               val        
--------            -------    
 1                  1          
 4                  2          
 8                  3
 20                 4          
 ...                ...
 500                100

I want to make a join so that “since” field from intervals table would be a lower bound for a “val”. And “since” values that have no “val” that is larger would not appear. See what I want to get:

since val
--------------
1     1
1     2
1     3
4     4
4     5
4     6
4     7
8     8
8     9
.....

How do I do it in generic SQL? Postgres-only solution will fit as well.

Answer 1

Credit to RhodiumToad on #postgresql

SELECT  * 
FROM    vals v 
JOIN    (select since
              , lead(since) over (order by since) as "end" 
         from intervals) s 
         ON ( v.val >= s.since 
             AND ((v.val >= s."end") IS NOT TRUE)
            )
;