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 TOP or
FETCH ROWS.
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
performed with arrange(), but it's not guaranteed. tail() is not
supported at all because the situation is even murkier for the "last" rows.
Usage
# S3 method for tbl_lazy
head(x, n = 6L, ...)Value
Another tbl_lazy. Use show_query() to see the generated
query, and use collect() to execute the query
and return data to R.
Examples
library(dplyr, warn.conflicts = FALSE)
db <- memdb_frame(x = 1:100)
db %>% head() %>% show_query()
#> <SQL>
#> SELECT `dbplyr_9Iljj7AHPg`.*
#> FROM `dbplyr_9Iljj7AHPg`
#> 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`