feat(add-data): Add script for SQL schema initialization

Since we are working with an Azure SQL database, we need to fill the
generated customer data in a fitting schema. The schema will be
described in more detail in an updated README file later.

The added script uses `pyodbc` to connect to the database and create the
tables. This requires a connection string, which will not be checked out
to this repo for security reasons and must be obtained separately.

Additionally, a script `test_sql_connection.py` is added with this
commit, which is a simple utility to test the `pyodbc` connection.

data_preparation/init_sql_schema.py

@@ -0,0 +1,111 @@
+"""Script to create the SQL schema in Azure SQL Database."""
+
+import os
+
+import pyodbc
+
+schema_creation = """
+CREATE TABLE Addresses (
+    ID INT PRIMARY KEY IDENTITY(1,1),
+    StreetName NVARCHAR(100),
+    HouseNumber NVARCHAR(10),
+    City NVARCHAR(50),
+    PostalCode NVARCHAR(10),
+    Longitude FLOAT,
+    Latitude FLOAT
+);
+
+CREATE TABLE Meters (
+    ID INT PRIMARY KEY IDENTITY(1,1),
+    Signature NVARCHAR(11),
+    MeterType NVARCHAR(3),
+    AddressID INT,
+    FOREIGN KEY (AddressID) REFERENCES Addresses(ID)
+);
+
+CREATE TABLE Customers (
+    ID INT PRIMARY KEY IDENTITY(1,1),
+    FirstName NVARCHAR(100),
+    LastName NVARCHAR(100),
+    GasMeterID INT,
+    EltMeterID INT,
+    FOREIGN KEY (GasMeterID) REFERENCES Meters(ID),
+    FOREIGN KEY (EltMeterID) REFERENCES Meters(ID)
+);
+
+CREATE TABLE Readings (
+    ID INT PRIMARY KEY IDENTITY(1,1),
+    CustomerID INT,
+    MeterID INT,
+    ReadingDate DATE,
+    ReadingValue INT,
+    FOREIGN KEY (CustomerID) REFERENCES Customers(ID),
+    FOREIGN KEY (MeterID) REFERENCES Meters(ID)
+);
+"""
+
+
+def create_tables(cursor: pyodbc.Cursor, schema: str) -> None:
+    """Create database tables based on the provided schema.
+
+    This function takes a database schema as a string and executes each table
+    creation statement separately. It handles cases where tables already exist
+    and reports this information.
+
+    Parameters
+    ----------
+    cursor : pyodbc.Cursor
+        A pyodbc cursor object used to execute SQL commands.
+    schema : str
+        A string containing SQL statements for table creation, separated by
+        semicolons.
+
+    Returns
+    -------
+    None
+        This function doesn't return any value.
+
+    Raises
+    ------
+    pyodbc.ProgrammingError
+        If there's an error in executing the SQL statements, other than
+        "table already exists".
+
+    Notes
+    -----
+    - The function assumes the existence of a global 'conn' object for
+      committing changes to the database.
+    - It prints a message if a table already exists instead of raising an error.
+    """
+    for table_creation in schema.split(";"):
+        if table_creation.strip():
+            try:
+                cursor.execute(table_creation)
+                conn.commit()
+            except pyodbc.ProgrammingError as e:
+                if "There is already an object named" in str(e):
+                    print(f"Table already exists: {table_creation.split('(')[0].split()[-1]}")
+                else:
+                    raise
+
+
+if __name__ == "__main__":
+
+    # Connect to the database
+    connection_string = os.environ.get("AZURE_SQL_CONNECTION_STRING")
+
+    try:
+        conn = pyodbc.connect(connection_string)
+        cursor = conn.cursor()
+        print("Connected to Azure SQL Database successfully!")
+
+        # Example query
+        create_tables(cursor, schema_creation)
+
+    except pyodbc.Error as e:
+        print(f"Error connecting to Azure SQL Database: {e}")
+    finally:
+        if "cursor" in locals():
+            cursor.close()
+        if "conn" in locals():
+            conn.close()

data_preparation/test_sql_connection.py

@@ -0,0 +1,56 @@
+"""Script to test connection to Azure SQL Database."""
+
+import os
+
+import pyodbc
+
+
+def test_connection() -> bool:
+    """Test the connection to Azure SQL Database.
+
+    This function attempts to establish a connection to an Azure SQL Database
+    using a connection string stored in the environment variable
+    'AZURE_SQL_CONNECTION_STRING'. It executes a simple query to verify
+    the connection and prints the result of the connection attempt.
+
+    Returns
+    -------
+    bool
+        True if the connection was successful and closed properly,
+        False if there was an error connecting to the database.
+
+    Notes
+    -----
+    - The function requires the 'AZURE_SQL_CONNECTION_STRING' environment
+      variable to be set with a valid connection string.
+    - It uses pyodbc to establish the database connection.
+    - The function prints success or error messages to stdout.
+    - In case of a successful connection, it executes "SELECT @@version;"
+      as a test query.
+    - The function ensures that both the cursor and the connection are
+      closed after the operation, regardless of its success or failure.
+    """
+    connection_string = os.environ.get("AZURE_SQL_CONNECTION_STRING")
+    try:
+        conn = pyodbc.connect(connection_string)
+        cursor = conn.cursor()
+        print("Connected to Azure SQL Database successfully!")
+
+        # Example query
+        cursor.execute("SELECT @@version;")
+
+    except pyodbc.Error as e:
+        print(f"Error connecting to Azure SQL Database: {e}")
+        return False
+
+    finally:
+        if "cursor" in locals():
+            cursor.close()
+        if "conn" in locals():
+            conn.close()
+
+    return True
+
+
+if __name__ == "__main__":
+    test_connection()