Database connections (DBI, RSQLite) in R Programming - Mini Project: Build & Apply

Database connections (DBI, RSQLite)

📖 Scenario: You are working on a small project where you need to store and retrieve data using a database. You will use R with the DBI and RSQLite packages to connect to a database, create a table, insert data, and then read it back.

🎯 Goal: Build a simple R script that connects to an SQLite database, creates a table, inserts some data, and then reads the data back to display it.

📋 What You'll Learn

Use the DBI package to connect to an SQLite database

Create a table called students with columns id (integer) and name (text)

Insert exactly three students with ids 1, 2, 3 and names 'Alice', 'Bob', 'Charlie'

Read the data back from the students table

Print the retrieved data

💡 Why This Matters

🌍 Real World

Databases are used everywhere to store data safely and efficiently. Knowing how to connect and interact with databases is essential for data analysis and application development.

💼 Career

Many data jobs require working with databases to extract, manipulate, and analyze data. Skills with DBI and SQLite in R are useful for data scientists, analysts, and developers.

1

Set up the database connection

Load the DBI and RSQLite packages, then create a connection called conn to an in-memory SQLite database using dbConnect().

R Programming

# Load DBI and RSQLite packages
# Create a connection called conn to an in-memory SQLite database
# Your code here

Hint

Use dbConnect() with RSQLite::SQLite() and the special string ":memory:" to create a temporary database.

2

Create the students table

Use dbExecute() with the connection conn to create a table called students with columns id as INTEGER and name as TEXT.

R Programming

library(DBI)
library(RSQLite)
conn <- dbConnect(RSQLite::SQLite(), ":memory:")
# Create a table called students with columns id (INTEGER) and name (TEXT)
# Your code here

Hint

Write a SQL command inside dbExecute() to create the table with the specified columns.

3

Insert data into the students table

Use dbExecute() with conn to insert three rows into the students table with these exact values: (1, 'Alice'), (2, 'Bob'), and (3, 'Charlie').

R Programming

library(DBI)
library(RSQLite)
conn <- dbConnect(RSQLite::SQLite(), ":memory:")
dbExecute(conn, "CREATE TABLE students (id INTEGER, name TEXT)")
# Insert three students with ids 1, 2, 3 and names 'Alice', 'Bob', 'Charlie'
# Your code here

Hint

Use a single INSERT INTO statement with multiple value tuples.

4

Read and print the data

Use dbGetQuery() with conn to select all rows from the students table into a variable called result. Then print result.

R Programming

library(DBI)
library(RSQLite)
conn <- dbConnect(RSQLite::SQLite(), ":memory:")
dbExecute(conn, "CREATE TABLE students (id INTEGER, name TEXT)")
dbExecute(conn, "INSERT INTO students (id, name) VALUES (1, 'Alice'), (2, 'Bob'), (3, 'Charlie')")
# Select all rows from students into result and print it
# Your code here

Hint

Use dbGetQuery() to run a SELECT statement and assign it to result. Then use print() to show the data.

Practice

1. What is the main purpose of dbConnect() in R when working with databases?

easy

A. To run a SQL query and get results

B. To close an open database connection

C. To open a connection to a database

D. To create a new table in the database

Solution

1. Step 1: Understand the role of dbConnect()

   dbConnect() is used to start a connection between R and a database so they can communicate.

2. Step 2: Differentiate from other functions

   dbDisconnect() closes connections, dbGetQuery() runs queries, and dbExecute() changes data. Only dbConnect() opens the connection.

3. Final Answer:

   To open a connection to a database -> Option C

4. Quick Check:

   dbConnect() = open connection [OK]

Hint: Remember: Connect opens, Disconnect closes [OK]

Common Mistakes:

• Confusing dbConnect() with dbDisconnect()
• Thinking dbConnect() runs queries
• Assuming dbConnect() creates tables

2. Which of the following is the correct syntax to connect to an SQLite database file named mydata.sqlite using DBI in R?

easy

A. dbConnect(SQLite::RSQLite(), file = "mydata.sqlite")

B. dbConnect(SQLite, "mydata.sqlite")

C. dbConnect(RSQLite, dbname = "mydata.sqlite")

D. dbConnect(RSQLite::SQLite(), dbname = "mydata.sqlite")

Solution

1. Step 1: Identify correct function usage

   The correct way is to call dbConnect() with the driver RSQLite::SQLite() and specify the database file with dbname.

2. Step 2: Check each option

   dbConnect(RSQLite::SQLite(), dbname = "mydata.sqlite") uses the correct driver and argument name. Options B, C, and D misuse the driver or argument names.

3. Final Answer:

   dbConnect(RSQLite::SQLite(), dbname = "mydata.sqlite") -> Option D

4. Quick Check:

   Correct driver and dbname argument = dbConnect(RSQLite::SQLite(), dbname = "mydata.sqlite") [OK]

Hint: Use RSQLite::SQLite() and dbname for file [OK]

Common Mistakes:

• Using wrong driver syntax
• Using 'file' instead of 'dbname'
• Omitting the namespace RSQLite::

3. What will be the output of the following R code?

library(DBI)
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbExecute(con, "CREATE TABLE test (id INTEGER, name TEXT)")
dbExecute(con, "INSERT INTO test VALUES (1, 'Alice'), (2, 'Bob')")
res <- dbGetQuery(con, "SELECT name FROM test WHERE id = 2")
print(res)
dbDisconnect(con)

medium

A. name
1 Bob

B. id name
1 2 Bob

C. Error: no such table: test

D. NULL

Solution

1. Step 1: Understand the code flow

   The code creates an in-memory SQLite database, makes a table 'test', inserts two rows, then queries the name where id=2.

2. Step 2: Predict the query result

   The query selects the 'name' column for id=2, which is 'Bob'. The printed result is a data frame with one row and one column 'name' containing 'Bob'.

3. Final Answer:

   name 1 Bob -> Option A

4. Quick Check:

   Query returns name 'Bob' for id=2 [OK]

Hint: SELECT returns matching rows as data frame [OK]

Common Mistakes:

• Expecting full row instead of selected column
• Confusing dbExecute with dbGetQuery output
• Forgetting to disconnect connection

4. Identify the error in the following R code snippet that tries to connect to an SQLite database and run a query:

library(DBI)
con <- dbConnect(RSQLite::SQLite(), "mydb.sqlite")
result <- dbGetQuery(con, "SELECT * FROM users")
dbDisconnect(con)

medium

A. dbDisconnect() should be called before dbGetQuery()

B. The database file name should be passed as dbname argument, not directly

C. dbGetQuery() cannot be used with SQLite

D. The library DBI is not needed for SQLite connections

Solution

1. Step 1: Check dbConnect() usage

   The SQLite file name must be passed as dbname = "mydb.sqlite", not as a positional argument.

2. Step 2: Verify other function calls

   Calling dbGetQuery() before dbDisconnect() is correct. dbGetQuery() works with SQLite. The DBI library is required.

3. Final Answer:

   The database file name should be passed as dbname argument, not directly -> Option B

4. Quick Check:

   Use dbname= for file in dbConnect() [OK]

Hint: Always name dbname argument in dbConnect() [OK]

Common Mistakes:

• Passing file name without dbname=
• Disconnecting before query
• Thinking DBI is unnecessary

5. You want to create a new SQLite database in R, add a table named employees with columns id (integer) and name (text), insert three employees, and then retrieve all names. Which sequence of commands correctly achieves this?

hard

A. con <- dbConnect(RSQLite::SQLite(), dbname = "company.sqlite")
dbExecute(con, "CREATE TABLE employees (id INTEGER, name TEXT)")
dbExecute(con, "INSERT INTO employees VALUES (1, 'Anna'), (2, 'Ben'), (3, 'Cara')")
names <- dbGetQuery(con, "SELECT name FROM employees")
dbDisconnect(con)
print(names)

B. con <- dbConnect(RSQLite::SQLite(), "company.sqlite")
dbExecute(con, "CREATE employees (id INTEGER, name TEXT)")
dbExecute(con, "INSERT INTO employees VALUES (1, 'Anna'), (2, 'Ben'), (3, 'Cara')")
names <- dbGetQuery(con, "SELECT name FROM employees")
dbDisconnect(con)
print(names)

C. con <- dbConnect(RSQLite::SQLite(), dbname = "company.sqlite")
dbExecute(con, "CREATE TABLE employees (id TEXT, name INTEGER)")
dbExecute(con, "INSERT INTO employees VALUES (1, 'Anna'), (2, 'Ben'), (3, 'Cara')")
names <- dbGetQuery(con, "SELECT id FROM employees")
dbDisconnect(con)
print(names)

D. con <- dbConnect(RSQLite::SQLite(), dbname = "company.sqlite")
dbExecute(con, "CREATE TABLE employees (id INTEGER, name TEXT)")
dbExecute(con, "INSERT INTO employees VALUES (1, 'Anna')")
dbExecute(con, "INSERT INTO employees VALUES (2, 'Ben')")
dbExecute(con, "INSERT INTO employees VALUES (3, 'Cara')")
names <- dbGetQuery(con, "SELECT id FROM employees")
dbDisconnect(con)
print(names)

Solution

1. Step 1: Identify correct sequence

   Use dbConnect(RSQLite::SQLite(), dbname = "company.sqlite"), CREATE TABLE employees (id INTEGER, name TEXT), multi-row INSERT INTO employees VALUES (1, 'Anna'), (2, 'Ben'), (3, 'Cara'), SELECT name FROM employees.

2. Step 2: Eliminate distractors

   B: No dbname=, missing TABLE. C: Wrong types (name INTEGER fails insert), selects id. D: Selects id instead of name.

3. Final Answer:

   dbConnect(RSQLite::SQLite(), dbname = "company.sqlite"), correct CREATE TABLE, multi-row INSERT, SELECT name -> Option A

4. Quick Check:

   dbname=, id INTEGER name TEXT, INSERT 3 rows, SELECT name [OK]

Hint: Insert multiple rows in one dbExecute for efficiency [OK]

Common Mistakes:

• Passing file name without dbname=
• Wrong SQL syntax for CREATE TABLE
• Mixing column types (id TEXT instead of INTEGER)
• Selecting id instead of name
• Forgetting to disconnect