问题描述
很抱歉，这个非常简单的问题，但是...
如何保存使用dbplyr构建的查询结果，而不会在内存中加载数据。
这是我尝试过的。
library(DBI)
library(odbc)
library(RPostgresql)
library(tidyverse)
library(magrittr)
#>
#> Attaching package: 'magrittr'
#> The following object is masked from 'package:purrr':
#>
#> set_names
#> The following object is masked from 'package:tidyr':
#>
#> extract
library(dbplyr)
#>
#> Attaching package: 'dbplyr'
#> The following objects are masked from 'package:dplyr':
#>
#> ident,sql
pgdrv <- dbDriver(drvName = "Postgresql")
con <-dbConnect(pgdrv,dbname="genomes",host="127.0.0.1",port=5432,user = 'rotifer')
mtcars %<>%
rownames_to_column()
dbWriteTable(con,"cars",mtcars)
#> [1] TRUE
dbmtcars <- tbl(con,"cars")
dbmtcars %>%
mutate(ts = cyl * carb) -> newtb
newtb %>% show_query()
#> <sql>
#> SELECT "row.names","rowname","mpg","cyl","disp","hp","drat","wt","qsec","vs","am","gear","carb","cyl" * "carb" AS "ts"
#> FROM "cars"
newtb %>% db_write_table(con,"newtb")
#> Error in UseMethod("db_write_table"): no applicable method for 'db_write_table' applied to an object of class "c('tbl_PostgresqlConnection','tbl_dbi','tbl_sql','tbl_lazy','tbl')"
由reprex package（v0.3.0）于2020-10-09创建
预先感谢
解决方法
我通过试探找到了答案，我不知道该怎么解释，但是可以解决问题。
我只是使用db_compute和db_sql_render来解决要执行并保存在新表中的查询。
db_compute(con=con,sql=db_sql_render(con,newtb),table="newtb")
完整的代码如下：
library(DBI)
library(odbc)
library(RPostgreSQL)
library(tidyverse)
library(magrittr)
#>
#> Attaching package: 'magrittr'
#> The following object is masked from 'package:purrr':
#>
#> set_names
#> The following object is masked from 'package:tidyr':
#>
#> extract
library(dbplyr)
#>
#> Attaching package: 'dbplyr'
#> The following objects are masked from 'package:dplyr':
#>
#> ident,sql
pgdrv <- dbDriver(drvName = "PostgreSQL")
con <-dbConnect(pgdrv,dbname="genomes",host="127.0.0.1",port=5432,user = 'rotifer')
mtcars %<>%
rownames_to_column()
#> [1] TRUE
dbmtcars <- tbl(con,"cars")
dbmtcars %>%
mutate(ts = cyl * carb) -> newtb
newtb %>% show_query()
#> <SQL>
#> SELECT "row.names","rowname","mpg","cyl","disp","hp","drat","wt","qsec","vs","am","gear","carb","cyl" * "carb" AS "ts"
#> FROM "cars"
db_compute(con=con,table="newtb")
#> [1] "newtb"
dbCommit(con)
#> [1] TRUE
sbpsigt <- tbl(con,"newtb")
sbpsigt
#> # Source: table<newtb> [?? x 14]
#> # Database: postgres 10.0.14 [rotifer@127.0.0.1:5432/genomes]
#> row.names rowname mpg cyl disp hp drat wt qsec vs am gear
#> <chr> <chr> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 1 Mazda … 21 6 160 110 3.9 2.62 16.5 0 1 4
#> 2 2 Mazda … 21 6 160 110 3.9 2.88 17.0 0 1 4
#> 3 3 Datsun… 22.8 4 108 93 3.85 2.32 18.6 1 1 4
#> 4 4 Hornet… 21.4 6 258 110 3.08 3.22 19.4 1 0 3
#> 5 5 Hornet… 18.7 8 360 175 3.15 3.44 17.0 0 0 3
#> 6 6 Valiant 18.1 6 225 105 2.76 3.46 20.2 1 0 3
#> 7 7 Duster… 14.3 8 360 245 3.21 3.57 15.8 0 0 3
#> 8 8 Merc 2… 24.4 4 147. 62 3.69 3.19 20 1 0 4
#> 9 9 Merc 2… 22.8 4 141. 95 3.92 3.15 22.9 1 0 4
#> 10 10 Merc 2… 19.2 6 168. 123 3.92 3.44 18.3 1 0 4
#> # … with more rows,and 2 more variables: carb <dbl>,ts <dbl>
dbDisconnect(con)
#> [1] TRUE
由reprex package（v0.3.0）于2020-10-09创建
,我使用以下模式保存构造的SQL表：
con <-dbConnect('you connection details here')
dbmtcars <- tbl(con,"cars")
newtb = dbmtcars %>% mutate(ts = cyl * carb)
sql_query <- "SELECT *\n","INTO db_name.schema_name.new_tbl_name\n","FROM (\n",dbplyr::sql_render(newtb ),"\n) AS alias")
dbExecute(db_connection,as.character(sql_query))
有关更多详细信息，请参见write_to_datebase函数here。