postgres-tables: Convenience functions for reading/writing DBMS tables

In RPostgres: C++ Interface to PostgreSQL

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)

RPostgres documentation built on Oct. 23, 2023, 1:06 a.m.