dbWriteTable: Copy data frames to database tables
In DBI: R Database Interface

dbWriteTable

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.

\Sexpr[results=rd,stage=render]{DBI:::methods_as_rd("dbWriteTable")}

Usage

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

Arguments

`conn`	A DBIConnection object, as returned by `dbConnect()`.
`name`	The table name, passed on to `dbQuoteIdentifier()`. Options are: a character string with the unquoted DBMS table name, e.g. `"table_name"`, a call to `Id()` with components to the fully qualified table name, e.g. `Id(schema = "my_schema", table = "table_name")` a call to `SQL()` with the quoted and fully qualified table name given verbatim, e.g. `SQL('"my_schema"."table_name"')`
`value`	A data.frame (or coercible to data.frame).
`...`	Other parameters passed on to methods.

Details

This function expects a data frame. Use dbWriteTableArrow() to write an Arrow object.

This function is useful if you want to create and load a table at the same time. Use dbAppendTable() or dbAppendTableArrow() for appending data to an existing table, dbCreateTable() or dbCreateTableArrow() for creating a table, and dbExistsTable() and dbRemoveTable() for overwriting tables.

DBI only standardizes writing data frames with dbWriteTable(). Some backends might implement methods that can consume CSV files or other data formats. For details, see the documentation for the individual methods.

Value

dbWriteTable() returns TRUE, invisibly.

Failure modes

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: FALSE)
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

The value argument must be a data frame with a subset of the columns of the existing table if append = TRUE. The order of the columns does not matter with append = TRUE.

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, in a pre-existing connection, and after reconnecting to the database.

SQL keywords can be used freely in table names, column names, and data. Quotes, commas, spaces, and other special characters such as newlines and tabs, 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,
- converted a character vector, which gives the full decimal representation
- written to another table and read again unchanged
character (in both UTF-8 and native encodings), supporting empty strings before and after a non-empty string
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), also for dates prior to 1970 or 1900 or after 2038
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), also for timestamps prior to 1970 or 1900 or after 2038 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. If a column is missed from field.types, the type is inferred from the input data with dbDataType().

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.

The default is row.names = FALSE.

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")

DBI documentation built on June 22, 2024, 9:41 a.m.