R: Copy data frames to database tables

dbWriteTable {DBI} | R Documentation

## Copy data frames to database tables

### Description

Writes, overwrites or appends a data frame to a database table, optionally converting row names to a column and specifying SQL data types for fields.

#### Methods in other packages

- `DBI::dbWriteTable("DBIConnection", "Id")`

### Usage

    dbWriteTable(conn, name, value, ...)

### Arguments

`conn` | A DBIConnection object, as returned by `dbConnect()`.
`name` | A character string specifying the unquoted DBMS table name, or the result of a call to `dbQuoteIdentifier()`.
`value` | a data.frame (or coercible to data.frame).
`...` | Other parameters passed on to methods.

### Value

`dbWriteTable()` returns `TRUE`, invisibly. If the table exists, and both `append` and `overwrite` arguments are unset, or `append = TRUE` and the data frame with the new data has different column names, an error is raised; the remote table remains unchanged.

An error is raised when calling this method for a closed or invalid connection. An error is also raised if `name` cannot be processed with `dbQuoteIdentifier()` or if this results in a non-scalar. Invalid values for the additional arguments `row.names`, `overwrite`, `append`, `field.types`, and `temporary` (non-scalars, unsupported data types, `NA`, incompatible values, duplicate or missing names, incompatible columns) also raise an error.

### Additional arguments

The following arguments are not part of the `dbWriteTable()` generic (to improve compatibility across backends) but are part of the DBI specification:

- `row.names` (default: `NA`)

- `overwrite` (default: `FALSE`)

- `append` (default: `FALSE`)

- `field.types` (default: `NULL`)

- `temporary` (default: `FALSE`)

They must be provided as named arguments. See the "Specification" and "Value" sections for details on their usage.

### Specification

The `name` argument is processed as follows, to support databases that allow non-syntactic names for their objects:

- If an unquoted table name as string: `dbWriteTable()` will do the quoting, perhaps by calling `dbQuoteIdentifier(conn, x = name)`

- If the result of a call to `dbQuoteIdentifier()`: no more quoting is done

If the `overwrite` argument is `TRUE`, an existing table of the same name will be overwritten. This argument doesn't change behavior if the table does not exist yet.

If the `append` argument is `TRUE`, the rows in an existing table are preserved, and the new data are appended. If the table doesn't exist yet, it is created.

If the `temporary` argument is `TRUE`, the table is not available in a second connection and is gone after reconnecting. Not all backends support this argument. A regular, non-temporary table is visible in a second connection and after reconnecting to the database.

SQL keywords can be used freely in table names, column names, and data. Quotes, commas, and spaces can also be used in the data, and, if the database supports non-syntactic identifiers, also for table names and column names.

The following data types must be supported at least, and be read identically with `dbReadTable()`:

- integer

- numeric (the behavior for `Inf` and `NaN` is not specified)

- logical

- `NA` as NULL

- 64-bit values (using `"bigint"` as field type); the result can be converted to a numeric, which may lose precision,

- character (in both UTF-8 and native encodings), supporting empty strings

- factor (returned as character)

- list of raw (if supported by the database)

- objects of type blob::blob (if supported by the database)

- date (if supported by the database; returned as `Date`)

- time (if supported by the database; returned as objects that inherit from `difftime`)

- timestamp (if supported by the database; returned as `POSIXct` respecting the time zone but not necessarily preserving the input time zone)

Mixing column types in the same table is supported.

The `field.types` argument must be a named character vector with at most one entry for each column. It indicates the SQL data type to be used for a new column.

The interpretation of rownames depends on the `row.names` argument, see `sqlRownamesToColumn()` for details:

- If `FALSE` or `NULL`, row names are ignored.

- If `TRUE`, row names are converted to a column named "row_names", even if the input data frame only has natural row names from 1 to `nrow(...)`.

- If `NA`, a column named "row_names" is created if the data has custom row names, no extra column is created in the case of natural row names.

- If a string, this specifies the name of the column in the remote table that contains the row names, even if the input data frame only has natural row names.

### See Also

Other DBIConnection generics: `DBIConnection-class`, `dbDataType`, `dbDisconnect`, `dbExecute`, `dbExistsTable`, `dbGetException`, `dbGetInfo`, `dbGetQuery`, `dbIsValid`, `dbListFields`, `dbListObjects`, `dbListResults`, `dbListTables`, `dbReadTable`, `dbRemoveTable`, `dbSendQuery`, `dbSendStatement`

### Examples

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

    dbWriteTable(con, "mtcars", mtcars[1:5, ])
    dbReadTable(con, "mtcars")

    dbWriteTable(con, "mtcars", mtcars[6:10, ], append = TRUE)
    dbReadTable(con, "mtcars")

    dbWriteTable(con, "mtcars", mtcars[1:10, ], overwrite = TRUE)
    dbReadTable(con, "mtcars")

    # No row names
    dbWriteTable(con, "mtcars", mtcars[1:10, ], overwrite = TRUE, row.names = FALSE)
    dbReadTable(con, "mtcars")

[Package DBI version 0.8 Index]