SQLite database for sensor data in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the SQLite library.

Raspberry Pi

import [1]

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

Asys

Bos

Csqlite3

Drandom

Attempts:

3 left

💡 Hint

Common Mistakes

Importing unrelated modules like os or sys.

We use the sqlite3 module to work with SQLite databases in Python.

2fill in blank

medium

Complete the code to connect to a database file named 'sensor_data.db'.

Raspberry Pi

conn = sqlite3.[1]('sensor_data.db')

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

Aconnect

Bopen

Cstart

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using open or create which are not SQLite connection methods.

The connect function opens a connection to the SQLite database file.

3fill in blank

hard

Fix the error in the SQL command to create a table named 'readings' with columns 'id' (integer primary key) and 'value' (real).

Raspberry Pi

cursor.execute('CREATE TABLE [1] (id INTEGER PRIMARY KEY, value REAL)')

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

Areadings

Bdata

Csensor

Dvalues

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect table names like 'data' or 'sensor'.

The table should be named readings as per the requirement.

4fill in blank

hard

Fill both blanks to insert a sensor value into the 'readings' table using a parameterized query.

Raspberry Pi

cursor.execute('INSERT INTO readings (value) VALUES ([1])', ([2],))

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

A?

Bsensor_value

C:value

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using literal values instead of placeholders.

Using incorrect variable names.

The question mark ? is a placeholder for the value, and sensor_value is the variable holding the data.

5fill in blank

hard

Fill all three blanks to commit the transaction, close the cursor, and close the connection.

Raspberry Pi

conn.[1]()
cursor.[2]()
conn.[3]()

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

Arollback

Bclose

Ccommit

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using rollback instead of commit.

Forgetting to close cursor or connection.

First, commit saves changes, then close the cursor and connection to free resources.

Practice

1. What is the main purpose of using SQLite on a Raspberry Pi for sensor data?

easy

A. To send sensor data directly to the cloud

B. To control the sensor hardware directly

C. To store sensor readings locally without needing a separate database server

D. To display sensor data on a web page automatically

Solution

1. Step 1: Understand SQLite's role on Raspberry Pi

   SQLite is a lightweight database that runs locally without needing a separate server.

2. Step 2: Connect SQLite to sensor data storage

   It stores sensor readings on the Raspberry Pi itself, making data management easy and offline.

3. Final Answer:

   To store sensor readings locally without needing a separate database server -> Option C

4. Quick Check:

   SQLite stores data locally = B [OK]

Hint: SQLite stores data locally on Pi, no extra server needed [OK]

Common Mistakes:

• Confusing SQLite with cloud services
• Thinking SQLite controls hardware
• Assuming SQLite automatically displays data

2. Which of the following is the correct Python code snippet to create a table named sensors with columns id (integer primary key), name (text), and value (real)?

easy

A. cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)')

B. cursor.execute('CREATE sensors TABLE (id INT, name STRING, value FLOAT)')

C. cursor.execute('MAKE TABLE sensors (id PRIMARY KEY, name TEXT, value REAL)')

D. cursor.execute('CREATE TABLE sensors id INTEGER, name TEXT, value REAL')

Solution

1. Step 1: Check SQL syntax for table creation

   The correct SQL command is CREATE TABLE followed by table name and column definitions in parentheses.

2. Step 2: Match Python sqlite3 syntax

   Python uses cursor.execute() with a valid SQL string. cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)') matches correct SQL and Python syntax.

3. Final Answer:

   cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)') -> Option A

4. Quick Check:

   Correct SQL CREATE TABLE syntax = D [OK]

Hint: Use 'CREATE TABLE table_name (columns)' inside cursor.execute() [OK]

Common Mistakes:

• Using wrong SQL keywords like MAKE TABLE
• Incorrect column types like STRING instead of TEXT
• Missing parentheses around columns

3. Given this Python code snippet using sqlite3 on Raspberry Pi:

import sqlite3
conn = sqlite3.connect('data.db')
cursor = conn.cursor()
cursor.execute('CREATE TABLE IF NOT EXISTS sensors (name TEXT, value REAL)')
cursor.execute("INSERT INTO sensors VALUES ('temp', 23.5)")
cursor.execute('SELECT * FROM sensors')
rows = cursor.fetchall()
print(rows)

What will be the output?

medium

A. [('temp', 23.5)]

B. []

C. SyntaxError

D. None

Solution

1. Step 1: Understand table creation and insertion

   The table 'sensors' is created if not exists, then a row ('temp', 23.5) is inserted.

2. Step 2: Fetch all rows and print

   The SELECT query fetches all rows, which includes the inserted row, so print outputs [('temp', 23.5)].

3. Final Answer:

   [('temp', 23.5)] -> Option A

4. Quick Check:

   Inserted row fetched = [('temp', 23.5)] [OK]

Hint: Inserted data appears in fetchall() output as list of tuples [OK]

Common Mistakes:

• Forgetting to insert data before SELECT
• Expecting empty list if table exists
• Confusing fetchall() output format

4. This Python code tries to insert sensor data but causes an error:

cursor.execute('CREATE TABLE sensors (name TEXT, value REAL)')
cursor.execute('INSERT INTO sensors (name, value) VALUES (?, ?)', ('humidity'))
conn.commit()

What is the error and how to fix it?

medium

A. Error: SQL syntax error; fix by removing parentheses in VALUES

B. Error: Missing second value in tuple; fix by adding a second value like ('humidity', 45.0)

C. Error: Table sensors does not exist; fix by creating table first

D. Error: commit() missing; fix by adding conn.commit()

Solution

1. Step 1: Identify parameter mismatch in INSERT

   The VALUES clause expects two values, but only one ('humidity') is given as a tuple missing a second element.

2. Step 2: Fix by providing both values

   Provide a tuple with two elements, e.g., ('humidity', 45.0), to match the two columns.

3. Final Answer:

   Error: Missing second value in tuple; fix by adding a second value like ('humidity', 45.0) -> Option B

4. Quick Check:

   Parameter count matches columns = C [OK]

Hint: Tuple for parameters must match number of placeholders [OK]

Common Mistakes:

• Passing single string instead of tuple with two values
• Ignoring commit() after insert
• Wrong SQL syntax in INSERT statement

5. You want to store sensor readings with a timestamp in SQLite on Raspberry Pi. Which table schema and insertion code correctly store sensor name, value, and current time using Python's sqlite3?

hard

A. CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, 'CURRENT_TIMESTAMP')")

B. CREATE TABLE readings (name TEXT, value REAL, time INTEGER); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, CURRENT_TIMESTAMP)")

C. CREATE TABLE readings (name TEXT, value REAL, time INTEGER); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now'))")

D. CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))")

Solution

1. Step 1: Choose correct table schema for timestamp

   Use TEXT type for time column to store datetime strings, which SQLite supports well.

2. Step 2: Insert current local time correctly

   Use SQLite function datetime('now', 'localtime') to get current local timestamp as text.

3. Step 3: Match insertion code with schema

   CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))") uses TEXT time column and inserts with datetime('now', 'localtime'), which is correct.

4. Final Answer:

   CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))") -> Option D

5. Quick Check:

   Local timestamp stored as TEXT = A [OK]

Hint: Use datetime('now', 'localtime') for current local time in SQLite [OK]

Common Mistakes:

• Using CURRENT_TIMESTAMP without quotes in Python
• Storing time as INTEGER without conversion
• Ignoring localtime adjustment for timestamps