Use LHS.* after left_join()

[mgirlich]

Closes #898. There should be no issues with Oracle this time as this uses a table alias.

library(dbplyr)

lf1 <- lazy_frame(!!!setNames(as.list(1:26), letters))
lf2 <- lazy_frame(a = 1, a1 = 1, a2 = 1)

lf1 |> 
  left_join(lf2)
#> Joining, by = "a"
#> <SQL>
#> SELECT `LHS`.*, `a1`, `a2`
#> FROM `df` AS `LHS`
#> LEFT JOIN `df` AS `RHS`
#>   ON (`LHS`.`a` = `RHS`.`a`)

# and a small bonus thanks to inlining `select()` into joins
lf1 |> 
  left_join(lf2) %>% 
  relocate(a1)
#> Joining, by = "a"
#> <SQL>
#> SELECT `a1`, `LHS`.*, `a2`
#> FROM `df` AS `LHS`
#> LEFT JOIN `df` AS `RHS`
#>   ON (`LHS`.`a` = `RHS`.`a`)

^{Created on 2022-08-04 by the reprex package (v2.0.1)}

[hadley]

Looks great!

[hadley]

Or inner join?

Could we apply the same logic to right joins too?

[mgirlich]

Not that simple to extend this to all type of joins but now they are all supported (note that for full_join() one can never use *).

[hadley]

If it's easy, maybe we should only use * if there is more than one variable selected?

[mgirlich]

Yes, this looks a bit better now.

[hadley]

Nice!