[bigger_cheese]

I mostly use SAS, I tend to prefer using plain sql queries where I typically depart SQL and jump into code is doing what SAS calls "By Group processing" (example https://support.sas.com/kb/26/013.html#)

I am not as familiar with R. Last time I worked in R (some years ago) equivalent R code was something like this caution I'm no expert in writing R so might be a better /more intuitive way...

Output_data <-merge(x=T1, y=T2, by="Date", all.x="True") %>% mutate(My_var = NAME) %>% fill(My_var)

In SQL the equivalent would need to use Over (Partition by) which is less intuitive for me to write.