Database connections (DBI, RSQLite) in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load the DBI package.

R Programming

library([1])

Drag options to blanks, or click blank then click option'

ADBI

BRSQLite

Cdplyr

Dggplot2

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to load RSQLite instead of DBI first.

The library() function loads the DBI package, which is needed to work with databases in R.

2fill in blank

medium

Complete the code to connect to an in-memory SQLite database.

R Programming

con <- DBI::dbConnect([1], ":memory:")

Drag options to blanks, or click blank then click option'

ARSQLite::SQLite()

BSQLite

CRSQLite

DDBI

Attempts:

3 left

💡 Hint

Common Mistakes

Passing just 'RSQLite' or 'SQLite' without calling the function.

The dbConnect() function needs the driver object from RSQLite, which is RSQLite::SQLite() for an SQLite database.

3fill in blank

hard

Fix the error in the code to disconnect from the database.

R Programming

DBI::dbDisconnect([1])

Drag options to blanks, or click blank then click option'

Aconnection

Bconn

Cdb

Dcon

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that was not defined for the connection.

The connection object was stored in the variable con. You must pass it to dbDisconnect() to close the connection.

4fill in blank

hard

Fill both blanks to create a table named 'people' with columns 'name' and 'age'.

R Programming

DBI::dbExecute(con, "CREATE TABLE [1] ([2] TEXT, age INTEGER)")

Drag options to blanks, or click blank then click option'

Apeople

Bperson

Cname

Dfullname

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular table name or wrong column name.

The table name is 'people' and the first column is 'name' of type TEXT.

5fill in blank

hard

Fill all three blanks to insert a person named 'Alice' aged 30 into the 'people' table.

R Programming

DBI::dbExecute(con, "INSERT INTO people ([1], age) VALUES ('[2]', [3])")

Drag options to blanks, or click blank then click option'

Aname

BAlice

C30

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing column names or values, or forgetting quotes around the name.

The column to insert is 'name', the value is 'Alice', and the age is 30.

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