R: Extend example to demonstrate both RPostgres and RPostgreSQL

by-language/r/Makefile

@@ -1,4 +1,5 @@
 install:
 
 test:
-	Rscript basic.r
+	Rscript basic_rpostgres.r
+	Rscript basic_rpostgresql.r

by-language/r/README.md

@@ -2,9 +2,10 @@
 
 ## About
 
-The file `basic.r` includes a basic example program that uses the R
-[RPostgreSQL] package, the canonical database interface and 'PostgreSQL'
-driver for 'R', to connect to CrateDB.
+The files `basic_rpostgres.r` and `basic_rpostgresql.r` include basic
+example programs that use the R packages [RPostgres] resp. [RPostgreSQL],
+the canonical database interfaces and 'PostgreSQL' drivers for 'R',
+to connect to CrateDB.
 
 ## Usage
 
@@ -13,9 +14,10 @@ Start a CrateDB instance for evaluation purposes.
 docker run -it --rm --publish=4200:4200 --publish=5432:5432 crate:latest
 ```
 
-Invoke example program.
+Invoke example programs.
 ```shell
-Rscript basic.r
+Rscript basic_rpostgres.r
+Rscript basic_rpostgresql.r
 ```
 
 Invoke software tests.
@@ -24,4 +26,5 @@ make test
 ```
 
 
+[RPostgres]: https://cran.r-project.org/web/packages/RPostgres/
 [RPostgreSQL]: https://cran.r-project.org/web/packages/RPostgreSQL/

by-language/r/basic_rpostgres.r

@@ -0,0 +1,43 @@
+# Install driver on demand.
+# RPostgres: C++ Interface to PostgreSQL
+# https://cran.r-project.org/web/packages/RPostgres/
+
+# Optionally install the PostgreSQL library.
+if (!requireNamespace("RPostgres", quietly = TRUE)) {
+    install.packages("RPostgres", repos="https://cran.r-project.org")
+}
+
+# Load the DBI and PostgreSQL libraries.
+library(DBI)
+library(RPostgres)
+drv <- Postgres()
+
+# Open a database connection, where `dbname` is the name of the CrateDB schema.
+conn <- dbConnect(drv,
+                  host = "localhost",
+                  port = 5432,
+                  sslmode = "disable",
+                  user = "crate",
+                  password = "crate",
+                  dbname = "doc",
+                  )
+on.exit(DBI::dbDisconnect(conn), add = TRUE)
+
+# Invoke a basic select query.
+res <- dbGetQuery(conn, "SELECT mountain, region, height FROM sys.summits ORDER BY height DESC LIMIT 10;")
+print(res)
+
+# Delete testdrive table when needed.
+if (dbExistsTable(conn, "r")) {
+    dbRemoveTable(conn, "r")
+}
+
+# Basic I/O.
+res <- dbSendQuery(conn, "CREATE TABLE r (id INT PRIMARY KEY, data TEXT);")
+dbClearResult(res)
+res <- dbSendQuery(conn, "INSERT INTO r (id, data) VALUES (42, 'foobar');")
+dbClearResult(res)
+res <- dbSendQuery(conn, "REFRESH TABLE r;")
+dbClearResult(res)
+res <- dbGetQuery(conn, "SELECT * FROM r;")
+print(res)

by-language/r/basic_rpostgresql.r

@@ -0,0 +1,39 @@
+# Install driver on demand.
+# RPostgreSQL: R Interface to the 'PostgreSQL' Database System
+# https://cran.r-project.org/web/packages/RPostgreSQL/
+
+# Optionally install the PostgreSQL library.
+if (!requireNamespace("RPostgreSQL", quietly = TRUE)) {
+    install.packages("RPostgreSQL", repos="https://cran.r-project.org")
+}
+
+# Load the DBI and PostgreSQL libraries.
+library(DBI)
+library(RPostgreSQL)
+drv <- RPostgreSQL::PostgreSQL()
+
+# Open a database connection, where `dbname` is the name of the CrateDB schema.
+conn <- dbConnect(drv,
+                 host = "localhost",
+                 port = 5432,
+                 user = "crate",
+                 password = "crate",
+                 dbname = "doc",
+                 )
+on.exit(DBI::dbDisconnect(conn), add = TRUE)
+
+# Invoke a basic select query.
+res <- dbGetQuery(conn, "SELECT mountain, region, height FROM sys.summits ORDER BY height DESC LIMIT 10;")
+print(res)
+
+# Delete testdrive table when needed.
+if (dbExistsTable(conn, "r")) {
+    dbRemoveTable(conn, "r")
+}
+
+# Basic I/O.
+res <- dbGetQuery(conn, "CREATE TABLE IF NOT EXISTS r (id INT PRIMARY KEY, data TEXT);")
+res <- dbGetQuery(conn, "INSERT INTO r (id, data) VALUES (42, 'foobar');")
+res <- dbGetQuery(conn, "REFRESH TABLE r;")
+res <- dbGetQuery(conn, "SELECT * FROM r;")
+print(res)