Subset the first rowsSource:
This is a method for the
head() generic. It is usually translated to the
LIMIT clause of the SQL query. Because
LIMIT is not an official part of
the SQL specification, some database use other clauses like
Note that databases don't really have a sense of row order, so what "first"
means is subject to interpretation. Most databases will respect ordering
arrange(), but it's not guaranteed.
tail() is not
supported at all because the situation is even murkier for the "last" rows.
# S3 method for tbl_lazy head(x, n = 6L, ...)
library(dplyr, warn.conflicts = FALSE) db <- memdb_frame(x = 1:100) db %>% head() %>% show_query() #> <SQL> #> SELECT `dbplyr_012`.* #> FROM `dbplyr_012` #> LIMIT 6 # Pretend we have data in a SQL server database db2 <- lazy_frame(x = 1:100, con = simulate_mssql()) db2 %>% head() %>% show_query() #> <SQL> #> SELECT TOP 6 `df`.* #> FROM `df`