How do I prevent duplicates from a SQL join?

I have the following tables:

customer:

id	customer_number	company	firstname	lastname	account_manager_email	email	comments	terms	tax_id_number	lead_source	default_catalog	credit_limit
99453	C00123456	Serenity Inc.	Malcom	Reynolds	[email protected]	[email protected]	The cap'n	1	NULL	NULL	12345	NULL
99468	C00123456	Serenity Inc.	Zoe	Washburne	[email protected]	[email protected]	NULL	1	NULL	NULL	NULL	NULL
99960	C00123456	Serenity Inc.	Hoban	Washburne	[email protected]	[email protected]	NULL	1	NULL	NULL	NULL	NULL
100088	C00123456	Serenity Inc.	Inara	Serra	[email protected]	[email protected]	NULL	1	NULL	NULL	12345	NULL

customer_address:

id	company	street	city	state_abbreviation	postcode	telephone	firstname	lastname	created_at
133996	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Malcom	Reynolds	2017-05-08 12:45:53.000
134452	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Accounts	Payable	2017-05-09 10:19:59.000
134961	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	REF	987654321	2017-05-09 10:19:59.000
134962	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	REF	192837465	2017-05-09 10:19:59.000
133995	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Accounts	Payable	2017-05-09 10:19:59.000
133669	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	REF	123456789	2017-05-18 10:29:42.000
133667	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Accounts	Payable	2017-05-18 07:56:45.000
133666	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Accounts	Payable	2017-05-31 07:56:46.000
133626	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	Accounts	Payable	2017-06-16 12:45:08.000
133668	Serenity, Inc	123 Any St.	Anytown	AX	12345	123-456-7890	REF	PO	2017-06-16 12:45:08.000

I'm running this query to generate a CSV that I can use to import the data into another system:

     SELECT '"' + CAST(c.customer_number AS VARCHAR) + '"' AS 'Customer Number',
            '"' + CAST(c.company AS VARCHAR) + '"' AS 'Company Name',
            '"' + CAST(a.street AS VARCHAR) + '"' AS 'Company Address Line 1',
            '"' + CAST(a.city AS VARCHAR) + '"' AS 'Company City',
            '"' + CAST(a.state_abbreviation AS VARCHAR) + '"' AS 'Company State',
            '"' + CAST(a.postcode AS VARCHAR) + '"' AS 'Company Zip Code',
            '"' + CAST(a.telephone AS VARCHAR) + '"' AS 'Company Phone',
            '"' + CAST(c.firstname AS VARCHAR) + '"' AS 'Contact First Name',
            '"' + CAST(c.lastname AS VARCHAR) + '"' AS 'Contact Last Name',
            '"' + CAST(c.account_manager_email AS VARCHAR) + '"' AS 'Account Manager Email',
            '"' + CAST(a.company AS VARCHAR) + '"' AS 'Contact Company Name',
            '"' + CAST(a.street AS VARCHAR) + '"' AS 'Contact Address Line 1',
            '"' + CAST(a.city AS VARCHAR) + '"' AS 'Contact City',
            '"' + CAST(a.state_abbreviation AS VARCHAR) + '"' AS 'Contact State',
            '"' + CAST(a.postcode AS VARCHAR) + '"' AS 'Contact Zip Code',
            '"' + CAST(a.telephone AS VARCHAR) + '"' AS 'Contact Phone',
            '"' + CAST(c.email AS VARCHAR) + '"' AS 'Contact Email',
            '"' + CAST(c.comments AS VARCHAR) + '"' AS 'Internal Notes',
            '"' + CAST(c.terms AS VARCHAR) + '"' AS 'Terms',
            '"' + CAST(c.tax_id_number AS VARCHAR) + '"' AS 'Tax ID (US)',
            '"' + CAST(c.lead_source AS VARCHAR) + '"' AS 'Lead Source',
            '"' + CAST(c.default_catalog AS VARCHAR) + '"' AS 'Catalog',
            '"' + CAST(c.credit_limit AS VARCHAR) + '"' AS 'Credit Limit'
       FROM customer c,
            customer_address a
      WHERE c.customer_number = 'C00123456'
        AND a.company = c.company
   ORDER BY c.customer_number,
            c.created_at;

However, when I run that query I get 40 rows back, ten for each entry in customer. I've tried different join types but the results are the same.

A lot of this is legacy data and so the only thing that I appear to reliably be able to join on is the company name ("Serenity, Inc.")

I actually need two versions of this output. The first is a single row for each company containing the entry with the oldest created_at value from the customer table. The second are all the other records.

Note: This is on SQL Server 2005 (I know... an upgrade is planned but I have to get through this first)

Solution

To remove your duplicates you need to enumerate each row and assign a value based on an ordering criteria.

You could do this easily using a cte - I believe they are available in SQL Server 2005, I am of course unable to check.

with c as(
  select *, Row_Number() over(partition by customer_number order by id) rn
  from customer
),
ca as (
  select *, Row_Number() over(partition by company order by created_at) rn
  from customer_address
)
select <columns>
from c join ca on c.company=ca.company
where c.rn=1 and ca.rn=1 and c.customer_number='C00123456'