R: Convenience functions for reading/writing DBMS tables

postgres-tables {RPostgres}

R Documentation

Convenience functions for reading/writing DBMS tables

Description

dbAppendTable() is overridden because RPostgres uses placeholders of the form $1, $2 etc. instead of ?.

dbWriteTable() executes several SQL statements that create/overwrite a table and fill it with values. RPostgres does not use parameterised queries to insert rows because benchmarks revealed that this was considerably slower than using a single SQL string.

Usage

## S4 method for signature 'PqConnection'
dbAppendTable(conn, name, value, copy = NULL, ..., row.names = NULL)

## S4 method for signature 'PqConnection,Id'
dbExistsTable(conn, name, ...)

## S4 method for signature 'PqConnection,character'
dbExistsTable(conn, name, ...)

## S4 method for signature 'PqConnection,Id'
dbListFields(conn, name, ...)

## S4 method for signature 'PqConnection,character'
dbListFields(conn, name, ...)

## S4 method for signature 'PqConnection'
dbListObjects(conn, prefix = NULL, ...)

## S4 method for signature 'PqConnection'
dbListTables(conn, ...)

## S4 method for signature 'PqConnection,character'
dbReadTable(conn, name, ..., check.names = TRUE, row.names = FALSE)

## S4 method for signature 'PqConnection,character'
dbRemoveTable(conn, name, ..., temporary = FALSE, fail_if_missing = TRUE)

## S4 method for signature 'PqConnection,character,data.frame'
dbWriteTable(
  conn,
  name,
  value,
  ...,
  row.names = FALSE,
  overwrite = FALSE,
  append = FALSE,
  field.types = NULL,
  temporary = FALSE,
  copy = NULL
)

## S4 method for signature 'PqConnection'
sqlData(con, value, row.names = FALSE, ...)

Arguments

`conn`	a PqConnection object, produced by `DBI::dbConnect()`
`name`	a character string specifying a table name. Names will be automatically quoted so you can use any sequence of characters, not just any valid bare table name. Alternatively, pass a name quoted with `dbQuoteIdentifier()`, an `Id()` object, or a string escaped with `SQL()`.
`value`	A data.frame to write to the database.
`copy`	If `TRUE`, serializes the data frame to a single string and uses `COPY name FROM stdin`. This is fast, but not supported by all postgres servers (e.g. Amazon's Redshift). If `FALSE`, generates a single SQL string. This is slower, but always supported. The default maps to `TRUE` on connections established via `Postgres()` and to `FALSE` on connections established via `Redshift()`.
`...`	Ignored.
`row.names`	Either `TRUE`, `FALSE`, `NA` or a string. If `TRUE`, always translate row names to a column called "row_names". If `FALSE`, never translate row names. If `NA`, translate rownames only if they're a character vector. A string is equivalent to `TRUE`, but allows you to override the default name. For backward compatibility, `NULL` is equivalent to `FALSE`.
`prefix`	A fully qualified path in the database's namespace, or `NULL`. This argument will be processed with `dbUnquoteIdentifier()`. If given the method will return all objects accessible through this prefix.
`check.names`	If `TRUE`, the default, column names will be converted to valid R identifiers.
`temporary`	If `TRUE`, only temporary tables are considered.
`fail_if_missing`	If `FALSE`, `dbRemoveTable()` succeeds if the table doesn't exist.
`overwrite`	a logical specifying whether to overwrite an existing table or not. Its default is `FALSE`.
`append`	a logical specifying whether to append to an existing table in the DBMS. Its default is `FALSE`.
`field.types`	character vector of named SQL field types where the names are the names of new table's columns. If missing, types are inferred with `DBI::dbDataType()`). The types can only be specified with `append = FALSE`.
`con`	A database connection.

Schemas, catalogs, tablespaces

Pass an identifier created with Id() as the name argument to specify the schema or catalog, e.g. name = Id(catalog = "my_catalog", schema = "my_schema", table = "my_table") . To specify the tablespace, use dbExecute(conn, "SET default_tablespace TO my_tablespace") before creating the table.

Examples


library(DBI)
con <- dbConnect(RPostgres::Postgres())
dbListTables(con)
dbWriteTable(con, "mtcars", mtcars, temporary = TRUE)
dbReadTable(con, "mtcars")

dbListTables(con)
dbExistsTable(con, "mtcars")

# A zero row data frame just creates a table definition.
dbWriteTable(con, "mtcars2", mtcars[0, ], temporary = TRUE)
dbReadTable(con, "mtcars2")

dbDisconnect(con)

[Package RPostgres version 1.4.3 Index]