CREATE TABLE IF NOT EXISTS customer_credit_entries (
  id BIGINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
  customer_id BIGINT UNSIGNED NOT NULL,
  invoice_id BIGINT UNSIGNED NULL,
  order_id BIGINT UNSIGNED NULL,
  entry_type ENUM('credit', 'debit') NOT NULL,
  amount DECIMAL(12,2) NOT NULL,
  description VARCHAR(255) NULL,
  created_by BIGINT UNSIGNED NULL,
  created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  CONSTRAINT fk_credit_customer FOREIGN KEY (customer_id) REFERENCES customers(id),
  CONSTRAINT fk_credit_invoice FOREIGN KEY (invoice_id) REFERENCES invoices(id) ON DELETE SET NULL,
  CONSTRAINT fk_credit_order FOREIGN KEY (order_id) REFERENCES orders(id) ON DELETE SET NULL,
  CONSTRAINT fk_credit_user FOREIGN KEY (created_by) REFERENCES users(id),
  INDEX idx_credit_customer (customer_id, created_at),
  INDEX idx_credit_invoice (invoice_id)
);