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Convenience functions for reading/writing DBMS tables

Source: R/dbAppendTable_PqConnection.R, R/dbExistsTable_PqConnection_Id.R, R/dbExistsTable_PqConnection_character.R, and 9 more
postgres-tables.Rd

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 PqConnection
dbAppendTable(conn, name, value, copy = NULL, ..., row.names = NULL)

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

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

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

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

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

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

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

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

# S4 method for 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 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)
#> character(0)
dbWriteTable(con, "mtcars", mtcars, temporary = TRUE)
dbReadTable(con, "mtcars")
#>     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
#> 1  21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
#> 2  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
#> 3  22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
#> 4  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
#> 5  18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
#> 6  18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
#> 7  14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
#> 8  24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
#> 9  22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
#> 10 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
#> 11 17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
#> 12 16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
#> 13 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3
#> 14 15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3
#> 15 10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
#> 16 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
#> 17 14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
#> 18 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
#> 19 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
#> 20 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
#> 21 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
#> 22 15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2
#> 23 15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2
#> 24 13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4
#> 25 19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2
#> 26 27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
#> 27 26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
#> 28 30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
#> 29 15.8   8 351.0 264 4.22 3.170 14.50  0  1    5    4
#> 30 19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6
#> 31 15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
#> 32 21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2

dbListTables(con)
#> [1] "mtcars"
dbExistsTable(con, "mtcars")
#> [1] TRUE

# A zero row data frame just creates a table definition.
dbWriteTable(con, "mtcars2", mtcars[0, ], temporary = TRUE)
dbReadTable(con, "mtcars2")
#>  [1] mpg  cyl  disp hp   drat wt   qsec vs   am   gear carb
#> <0 rows> (or 0-length row.names)

dbDisconnect(con)