Question

Table Sufix:
id, name

(3, 'com')

Table DomainName:
id, name

(2, 'microsoft')

Table Domain:
id, name_code, sufix

(1, 2, 3)    -- microsoft.com

Table SubDomainName:

(4, 'windows')

Table SubDomain:
id, name_code, domain

(7, 4, 1)     -- windows.microsoft.com

Table Email:
id, name, atserver

(3, 'myemail', 7)    -- [e-mail]
(4, 'other', 1)      -- [e-mail]

Here is a problem of foreign key constraints. How can I resolve domains and subdomains to create emails correctly? I’m having problems with Unique INDEX with NULL values, for example, a solution maybe:

Table Email:
id, name, subdomain, domain

(3, 'myemail', 7, NULL)  -- [e-mail]
(4, 'other', NULL, 1)    -- [e-mail]

BUT

(5, 'newemail', NULL, NULL)  -- will duplicated values in the table
(6, 'newemail', NULL, NULL)
(7, 'newemail', NULL, NULL)
(8, 'newemail', NULL, NULL)

AND

(**3**, 'myemail', 7, 1)   -- [e-mail] and [e-mail]

Answer 1

How about (5, ‘newemail’, domain_id/subdomain_id, ‘domain/subdomain’)

So you could have

(5, ‘newemail’, 7, ‘subdomain’) or (5, ‘newemail’, 1, ‘domain’)

YOu could still LEFT JOIN SubDomain and Domain table but you will get only the data from the one that you need based on the ‘domain/subdomain’ field.

That is the quick solution. IMHO your DB structure is not very good and could be optimized. You should keep all domain/subdomain records in one table and use it for the emails. The table should be Table FullDomain: id, name_code, domain_name, subdomain_name


(1, 3, 2, 4) -- windows.microsoft.com


or


(1, 3, 2, 0) -- microsoft.com