join_by(): Syntax for generic joins

[krlmlr]

#557 (comment) and #378 (comment) propose a syntax for generic and rolling joins:

left_join( 
  FundMonths, Returns, 
  join_by(FundID == FundID, yearmonth > gmonth + 3, yearmonth <= gmonth + 15)
)

left_join( 
  events, days,
  join_by(collector_id == collector_id, event_timestamp >= largest(day))
)

As usual, this should be powered by an SE version join_by_().

We can pass this to the SQL engine (and perhaps to data tables) with relatively little work, the main challenge will be to implement this for data frames.

[ywhcuhk]

any progress on this feature?

[001ben]

Bump, would love to see this flow through to sparklyr in particular

[dholstius]

Would this cover wildcard joins as well?

[krlmlr]

Need to keep in mind that dbplyr now translates full joins with by = c() as cross joins (tidyverse/dbplyr@3316463).