SQLite database for sensor data in Raspberry Pi

Introduction

We use an SQLite database to save sensor readings so we can keep track of data over time. It helps us organize and find sensor information easily.

You want to store temperature readings from a sensor every minute.

You need to keep a history of humidity levels to analyze later.

You want to save light sensor data to check patterns during the day.

You want to log sensor data on a Raspberry Pi without needing a big database server.

Syntax

Raspberry Pi

import sqlite3

# Connect to database (creates file if not exists)
conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()

# Create table for sensor readings
cursor.execute('''
CREATE TABLE IF NOT EXISTS readings (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sensor_name TEXT NOT NULL,
    value REAL NOT NULL,
    timestamp DATETIME DEFAULT CURRENT_TIMESTAMP
)
''')

# Insert a sensor reading
cursor.execute('INSERT INTO readings (sensor_name, value) VALUES (?, ?)', ('temperature', 23.5))
conn.commit()

# Query data
cursor.execute('SELECT * FROM readings')
rows = cursor.fetchall()

# Close connection
conn.close()

Use sqlite3.connect() to open or create the database file.

Use cursor.execute() to run SQL commands like creating tables or inserting data.

Examples

This creates a table named readings if it does not exist yet.

Raspberry Pi

cursor.execute('CREATE TABLE IF NOT EXISTS readings (id INTEGER PRIMARY KEY, sensor_name TEXT, value REAL, timestamp DATETIME)')

This adds a new humidity reading with value 45.2.

Raspberry Pi

cursor.execute('INSERT INTO readings (sensor_name, value) VALUES (?, ?)', ('humidity', 45.2))

This gets all temperature readings from the database.

Raspberry Pi

cursor.execute('SELECT * FROM readings WHERE sensor_name = ?', ('temperature',))
rows = cursor.fetchall()

Sample Program

This program creates a database and table, inserts three temperature readings with a pause between them, then prints all stored readings with their timestamps.

Raspberry Pi

import sqlite3
import time

# Connect to SQLite database file
conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()

# Create table if not exists
cursor.execute('''
CREATE TABLE IF NOT EXISTS readings (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sensor_name TEXT NOT NULL,
    value REAL NOT NULL,
    timestamp DATETIME DEFAULT CURRENT_TIMESTAMP
)
''')

# Simulate inserting 3 temperature readings
for temp in [22.4, 22.8, 23.1]:
    cursor.execute('INSERT INTO readings (sensor_name, value) VALUES (?, ?)', ('temperature', temp))
    conn.commit()
    time.sleep(1)  # wait 1 second to get different timestamps

# Retrieve and print all readings
cursor.execute('SELECT id, sensor_name, value, timestamp FROM readings')
rows = cursor.fetchall()
for row in rows:
    print(f'ID: {row[0]}, Sensor: {row[1]}, Value: {row[2]}, Time: {row[3]}')

# Close connection
conn.close()

Important Notes

SQLite stores the database in a single file, making it easy to move or backup.

Always call conn.commit() after inserting or changing data to save it.

Use DEFAULT CURRENT_TIMESTAMP to automatically save the time when data is added.

Summary

SQLite helps save sensor data on Raspberry Pi without extra setup.

Create tables to organize sensor readings with columns for name, value, and time.

Insert and query data easily using Python's sqlite3 module.

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