r - 使用 dplyr 在数据库中写入表

Question

有没有办法让 dplyr 连接到数据库管道数据到该数据库内的新表，而不是在本地下载数据？

我想按照以下方式做一些事情:

tbl(con, "mytable") %>%
   group_by(dt) %>%
   tally() %>%
   write_to(name = "mytable_2", schema = "transformed")

Answer 1

虽然我完全同意学习 SQL 的建议，但您可以利用 dplyr 在绝对必要时才拉取数据这一事实，并使用 dplyr 构建查询，添加 TO TABLE 子句，然后使用 dplyr::do() 运行 SQL 语句，如:

# CREATE A DATABASE WITH A 'FLIGHTS' TABLE
library(RSQLite)
library(dplyr)
library(nycflights13)
my_db <- src_sqlite("~/my_db.sqlite3", create = T)
flights_sqlite <- copy_to(my_db, flights, temporary = FALSE, indexes = list(
  c("year", "month", "day"), "carrier", "tailnum"))

# BUILD A QUERY
QUERY = filter(flights_sqlite, year == 2013, month == 1, day == 1) %>%
    select( year, month, day, carrier, dep_delay, air_time, distance) %>%
    mutate( speed = distance / air_time * 60) %>%
    arrange( year, month, day, carrier)

# ADD THE "TO TABLE" CLAUSE AND EXECUTE THE QUERY 
do(paste(unclass(QUERY$query$sql), "TO TABLE foo"))

您甚至可以编写一个小函数来执行此操作:

to_table  <- function(qry,tbl)
    dplyr::do(paste(unclass(qry$query$sql), "TO TABLE",tbl))

并将查询通过管道传递给该函数，如下所示:

filter(flights_sqlite, year == 2013, month == 1, day == 1) %>%
    select( year, month, day, carrier, dep_delay, air_time, distance) %>%
    mutate( speed = distance / air_time * 60) %>%
    arrange( year, month, day, carrier) %>%
    to_table('foo')