merging datasets with interval dates and unbalanced panel

[LEILA BEN AOUN]

Hi stata users,
I face a problem I try to find an "easy" way to merge two datasets, one having a variable that varies over time and another one with time period.
I have an unbalanced panel
I will illustrate :
dataset1

Id	activity	begin_date	end_date
A	a1	1975m1	2001m5
A	a2	2001m6	2099m12
B	a1	1975m1	2013m5
C	a2	1999m7	2001m6
C	a3	2001m7	2012m12
C	a4	2013m1	2015m11

dataset2

Id	period	expenses
A	2000m12	100
A	2001m1	200
A	2001m2	300
A	2001m3	350
A	2001m4	400
A	2001m5	1000
A	2001m6	1500
A	2001m7	1800
B	2001m1	200
B	2001m2	900
...	...	...
C	2001m5	200
C	2001m6	250
C	2001m7	300
...
C	2012m11	800
C	2012m12	900
C	2013m1	700
C	2013m2	500
C	2013m3	400
C	2013m4	120

and I want in the end to have ... Result wanted

Id	period	expenses	activity
A	2000m12	100	a1
A	2001m1	200	a1
A	2001m2	300	a1
A	2001m3	350	a1
A	2001m4	400	a1
A	2001m5	1000	a1
A	2001m6	1500	a2
A	2001m7	1800	a2
B	2001m1	200	a1
B	2001m2	900	a1
...	...	...	...
C	2001m5	200	a2
C	2001m6	250	a2
C	2001m7	300	a3
...	...	...	...
C	2012m11	800	a3
C	2012m12	900	a3
C	2013m1	700	a4
C	2013m2	500	a4
C	2013m3	400	a4
C	2013m4	120	a4

I know that with sql we can say that period must be between begin_date and end_date .. but I could not find a trick to do this in stata.
The only way I found was to create 3fake lines" on dataset1 with

tsfill

and

carryforward

to have one observation each month-year but it duplicates to 60 Mio observations on my datasets and goes to 2Go ...
Thanks in advance for your time and proposal.

[Clyde Schechter]

You can do this with -rangejoin-, written by Robert Picard, available from SSC. To use -rangejoin- you also need -rangestat-, by Robert Picard, Nick Cox, and Roberto Ferrer, also available from SSC.

[LEILA BEN AOUN]

thank you I will try it tomorrow morning