Create Payment Reminder

Hi, all. I would like to create a payment reminder for a customer. May I  know whether below sql already included all outstanding AR transaction for a customer?

SELECT a.customer_id,

  a.customer_name,

  a.customer_number,

  b.site_use_id,

  c.trx_number,

  NULL rec_num,

  c.trx_date xdate,

  c.set_of_books_id,

  c.status_trx,

  c.doc_sequence_value,

  d.description,

  d.extended_amount * NVL (c.exchange_rate, 1) debit_amount,

  0 credit_amount,

  e.cust_trx_type_id trx_type_id,

  e.NAME invoice_type,

  z.segment2,

  c.invoice_currency_code curr,

  c.ct_reference REF,