Create an aggregated population table by region.
db_create_reg_pop_table(
pop_table,
cl_table,
pip_years,
region_code = c("pcn_region_code", "region_code")
)
data.table: A table with population data.
data.table: A table with country metadata.
numeric: A vector with calender years used in PIP.
character: A value with the region code column to use.
data.table