Question

有没有办法让 dplyr 连接数据库管道数据到该数据库中的新表，从不在本地下载数据？

我想按照以下方式做点什么：

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不会提取数据直到它必须使用dplyr构建查询的事实，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"))

你甚至可以写一点功能：

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

并将查询传递到该函数中，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')

用dplyr在数据库中写表

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