src_dbi {dplyr} | R Documentation

## Source for database backends

### Description

For backward compatibility dplyr provides three srcs for popular open source databases:

- `src_mysql()` connects to a MySQL or MariaDB database using `RMySQL::MySQL()`.

- `src_postgres()` connects to PostgreSQL using `RPostgreSQL::PostgreSQL()`

- `src_sqlite()` to connect to a SQLite database using `RSQLite::SQLite()`.

However, modern best practice is to use `tbl()` directly on an `DBIConnection`.

### Usage

    src_mysql(dbname, host = NULL, port = 0L, username = "root",
      password = "", ...)

    src_postgres(dbname = NULL, host = NULL, port = NULL, user = NULL,
      password = NULL, ...)

    src_sqlite(path, create = FALSE)

### Arguments

`dbname` | Database name
`host, port` | Host name and port number of database
`...` | for the src, other arguments passed on to the underlying database connector, `DBI::dbConnect()`. For the tbl, included for compatibility with the generic, but otherwise ignored.
`user, username, password` | User name and password. Generally, you should avoid saving username and password in your scripts as it is easy to accidentally expose valuable credentials. Instead, retrieve them from environment variables, or use database specific credential scores. For example, with MySQL you can set up `my.cnf` as described in `RMySQL::MySQL()`.
`path` | Path to SQLite database. You can use the special path ":memory:" to create a temporary in memory database.
`create` | if `FALSE`, `path` must already exist. If `TRUE`, will create a new SQlite3 database at `path` if `path` does not exist and connect to the existing database if `path` does exist.

### Details

All data manipulation on SQL tbls are lazy: they will not actually run the query or retrieve the data unless you ask for it: they all return a new `tbl_dbi` object. Use `compute()` to run the query and save the results in a temporary in the database, or use `collect()` to retrieve the results to R. You can see the query with `show_query()`.

For best performance, the database should have an index on the variables that you are grouping by. Use `explain()` to check that the database is using the indexes that you expect.

There is one excpetion: `do()` is not lazy since it must pull the data into R.

### Value

An S3 object with class `src_dbi`, `src_sql`, `src`.

### Examples

    # Basic connection using DBI -------------------------------------------
    if (require(dbplyr, quietly = TRUE)) {

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

    DBI::dbListTables(con)

    # To retrieve a single table from a source, use `tbl()`
    con %>% tbl("mtcars")

    # You can also use pass raw SQL if you want a more sophisticated query
    con %>% tbl(sql("SELECT * FROM mtcars WHERE cyl == 8"))

    # To show off the full features of dplyr's database integration,
    # we'll use the Lahman database. lahman_sqlite() takes care of
    # creating the database.
    lahman_p <- lahman_sqlite()
    batting <- lahman_p %>% tbl("Batting")
    batting

    # Basic data manipulation verbs work in the same way as with a tibble
    batting %>% filter(yearID > 2005, G > 130)
    batting %>% select(playerID:lgID)
    batting %>% arrange(playerID, desc(yearID))
    batting %>% summarise(G = mean(G), n = n())

    # There are a few exceptions. For example, databases give integer results
    # when dividing one integer by another. Multiply by 1 to fix the problem
    batting %>%
      select(playerID:lgID, AB, R, G) %>%
      mutate(
       R_per_game1 = R / G,
       R_per_game2 = R * 1.0 / G
     )

    # All operations are lazy: they don't do anything until you request the
    # data, either by `print()`ing it (which shows the first ten rows),
    # or by `collect()`ing the results locally.
    system.time(recent <- filter(batting, yearID > 2010))
    system.time(collect(recent))

    # You can see the query that dplyr creates with show_query()
    batting %>%
      filter(G > 0) %>%
      group_by(playerID) %>%
      summarise(n = n()) %>%
      show_query()
    }

[Package dplyr version 0.7.0 Index]