README.Rmd

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# dbplyr <a href='https://dbplyr.tidyverse.org'><img src='man/figures/logo.png' align="right" height="139" /></a>

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## Overview

dbplyr is the database backend for [dplyr](https://dplyr.tidyverse.org). It allows you to use remote database tables as if they are in-memory data frames by automatically converting dplyr code into SQL. 

To learn more about why you might use dbplyr instead of writing SQL, see `vignette("sql")`. To learn more about the details of the SQL translation, see `vignette("translation-verb")` and `vignette("translation-function")`.

## Installation

```{r, eval = FALSE}
# The easiest way to get dbplyr is to install the whole tidyverse:
install.packages("tidyverse")

# Alternatively, install just dbplyr:
install.packages("dbplyr")

# Or the the development version from GitHub:
# install.packages("devtools")
devtools::install_github("tidyverse/dbplyr")
```

## Usage

dbplyr is designed to work with database tables as if they were local data frames. To demonstrate this I'll first create an in-memory SQLite database and copy over a dataset:

```{r setup}
library(dplyr, warn.conflicts = FALSE)

con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
copy_to(con, mtcars)
```

Note that you don't actually need to load dbplyr with `library(dbplyr)`; dplyr automatically loads it for you when it sees you working with a database. Database connections are coordinated by the DBI package. Learn more at <https://dbi.r-dbi.org/>

Now you can retrieve a table using `tbl()` (see `?tbl_dbi` for more details). Printing it just retrieves the first few rows:

```{r}
mtcars2 <- tbl(con, "mtcars")
mtcars2
```

All dplyr calls are evaluated lazily, generating SQL that is only sent to the database when you request the data.

```{r}
# lazily generates query
summary <- mtcars2 %>% 
  group_by(cyl) %>% 
  summarise(mpg = mean(mpg, na.rm = TRUE)) %>% 
  arrange(desc(mpg))

# see query
summary %>% show_query()

# execute query and retrieve results
summary %>% collect()
```

## Code of Conduct

Please note that the dbplyr project is released with a [Contributor Code of Conduct](https://dbplyr.tidyverse.org/CODE_OF_CONDUCT.html). By contributing to this project, you agree to abide by its terms.