Table key in from-to form

We have metodology like this (around 500.000 rows and over 2000 met variables):
met1    rn1    1.1.2014      1.1.2028
met1    rn1    1.1.2018      1.1.2020
met1    rn2    1.1.2016      1.1.2028
met2    rn1    1.1.2016      1.1.2028
met2    rn2    1.1.2016      1.1.2028
Dates are dates when that specific rn is valid.

we have another table with amount for every rn (around 150.000.000 rows):
1.1.2014    rn1     100,8
1.1.2014    rn2     20,8
1.1.2014    rn3     36,7
1.1.2020    rn1     38,2
1.1.2020    rn2     111
1.1.2020    rn3     95,2

and I want to know how much is every met based on rn included,
for example:
1.1.2020 met1 149,2 =38,2+111
1.1.2014 met2 100,8

If it wasn't clear, please tell me to explain better, and thx in advance!