- Band join
- or range join.
A theta join could use any other operator than the equal operator.
A theta may not have any join key in the sql but you still have a join physically (ie when running the sql).
Physically, the join of R1 and R2 with the condition theta is the same than the selection of the cross product of R1 and R2 with the condition theta.
Find all customer in a age range
Find all the hospitals within 5 miles of a school
select distinct h.name from hospitals h, schools s where distance(h.location,s.location) < 5
Find all user clicks made within 5 seconds of page load
select * from Clicks c, PageLoads p where abs(c.click_time - p.load_time) < 5