Nicer conditional SQL

[mgirlich]

This slightly improves the SQL translations of is.na(), if(), ifelse(), if_else() and case_when()

Before

library(dbplyr, warn.conflicts = FALSE)
translate_sql(ifelse(is.na(x), 0L, 1L))
#> <SQL> CASE WHEN (((`x`) IS NULL)) THEN (0) WHEN NOT(((`x`) IS NULL)) THEN (1) END

translate_sql(case_when(is.na(x) ~ 0L, TRUE ~ 1L))
#> <SQL> CASE
#> WHEN (((`x`) IS NULL)) THEN (0)
#> ELSE (1)
#> END

After

library(dbplyr, warn.conflicts = FALSE)
translate_sql(ifelse(is.na(x), 0L, 1L))
#> <SQL> CASE WHEN ((`x` IS NULL)) THEN 0 WHEN NOT ((`x` IS NULL)) THEN 1 END

translate_sql(case_when(is.na(x) ~ 0L, TRUE ~ 1L))
#> <SQL> CASE WHEN ((`x` IS NULL)) THEN 0 ELSE 1 END

[mgirlich]

I had to change from enexpr() to enquo() due to an issue with the pipe: translate_sql(x %>% ifelse(1, 2)) didn't work but it does now.