Simplify database schema: remove card_type, card_id, add card_number

Refactor the database schema to better model the data relationships:

Schema changes:
- Removed cards.card_type (redundant, identical to card_number)
- Removed transactions.card_id (unnecessary indirection)
- Added transactions.card_number (stores card number for all transactions)
- Made cards.customer_id NOT NULL (every card must belong to a customer)
- Made transactions.customer_id nullable (NULL for anonymized transactions)

Import logic changes:
- Only create cards for known customers (transactions with customer_number)
- Store card_number for ALL transactions (including anonymized)
- Skip cards/customer creation for anonymized transactions

Additional changes:
- Add 'db reset' command to drop and recreate database
- Update migration file with new schema

This simplifies queries and better reflects the data model:
- Cards table: authoritative mapping of card_number -> customer_id
- Transactions table: stores all raw data including anonymized cards
- Customer relationship via JOIN on card_number for known customers

migrations/002_schema.sql

@@ -13,13 +13,12 @@ CREATE TABLE IF NOT EXISTS customers (
 CREATE TABLE IF NOT EXISTS cards (
     id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
     card_number VARCHAR(50) NOT NULL UNIQUE,
-    card_type VARCHAR(50),
-    customer_id INT UNSIGNED NULL,
+    customer_id INT UNSIGNED NOT NULL,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
     INDEX idx_card_number (card_number),
     INDEX idx_customer_id (customer_id),
-    FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL
+    FOREIGN KEY (customer_id) REFERENCES customers(id)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
 CREATE TABLE IF NOT EXISTS transactions (
@@ -31,19 +30,17 @@ CREATE TABLE IF NOT EXISTS transactions (
     price DECIMAL(8,4) NOT NULL,
     quality_code INT NOT NULL,
     quality_name VARCHAR(50) NOT NULL,
+    card_number VARCHAR(50) NOT NULL,
     station VARCHAR(20) NOT NULL,
     terminal VARCHAR(10) NOT NULL,
     pump VARCHAR(10) NOT NULL,
     receipt VARCHAR(20) NOT NULL,
     control_number VARCHAR(20),
-    card_id INT UNSIGNED NOT NULL,
     customer_id INT UNSIGNED NULL,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     INDEX idx_transaction_date (transaction_date),
     INDEX idx_batch_number (batch_number),
-    INDEX idx_card_id (card_id),
     INDEX idx_customer_id (customer_id),
-    INDEX idx_station (station),
-    FOREIGN KEY (card_id) REFERENCES cards(id),
-    FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL
+    INDEX idx_card_number (card_number),
+    INDEX idx_station (station)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;