Specifying join keys and their matching conditions

When both keys have the same name(s): just provide the key name(s).

flights2 |>
  left_join(planes, join_by(tailnum))

## # A tibble: 336,776 × 14
##   year.x time_hour           origin dest  tailnum carrier year.y type           
##    <int> <dttm>              <chr>  <chr> <chr>   <chr>    <int> <chr>          
## 1   2013 2013-01-01 05:00:00 EWR    IAH   N14228  UA        1999 Fixed wing mul…
## 2   2013 2013-01-01 05:00:00 LGA    IAH   N24211  UA        1998 Fixed wing mul…
## 3   2013 2013-01-01 05:00:00 JFK    MIA   N619AA  AA        1990 Fixed wing mul…
## 4   2013 2013-01-01 05:00:00 JFK    BQN   N804JB  B6        2012 Fixed wing mul…
## # ℹ 336,772 more rows
## # ℹ 6 more variables: manufacturer <chr>, model <chr>, engines <int>,
## #   seats <int>, speed <int>, engine <chr>