Question

The following query returns a single row, as desired. The ‘contracts’ table has 6 fields, each with a different username in it, for which I want to retrieve first/last names from a separate ‘users’ table. This works fine, but is there something more concise? I’m think the solution must be something using GROUP BY contracts.id to keep it one row, but I can’t seem to find anything better than this slew of sub-selects.

Help!

SELECT contracts.field1, contracts.field2,  (SELECT first_name FROM users WHERE username = service_provider_1), (SELECT last_name FROM users WHERE username = service_provider_1), (SELECT first_name FROM users WHERE username = service_provider_2), (SELECT last_name FROM users WHERE username = service_provider_2), (SELECT first_name FROM users WHERE username = service_org_business_contact), (SELECT last_name FROM users WHERE username = service_org_business_contact), (SELECT first_name FROM users WHERE username = client_service_contact_1), (SELECT last_name FROM users WHERE username = client_service_contact_1), (SELECT first_name FROM users WHERE username = client_service_contact_2), (SELECT last_name FROM users WHERE username = client_service_contact_2), (SELECT first_name FROM users WHERE username = client_business_contact), (SELECT last_name FROM users WHERE username = client_business_contact) FROM contracts WHERE id = ? 

It wouldn’t be so bad if I could get both first/last name from a single sub-select… so even with a cruddy sub-select solution I have twice the verbosity I should think I need…

EDIT: I get it now. The answer to being able to join to the same table multiple times is to use an alias for the table. Thank folks! New code is:

SELECT contracts.field1, contracts.field2,  sp1.first_name, sp1.last_name,  sp2.first_name, sp2.last_name,  sobc.first_name, sobc.last_name,  csc1.first_name, csc1.last_name,  csc2.first_name, csc2.last_name,  cbc.first_name, cbc.last_name FROM contracts JOIN users AS sp1 ON service_provider_1 = sp1.username JOIN users AS sp2 ON service_provider_2 = sp2.username JOIN users AS sobc ON service_org_business_contact = sobc.username JOIN users AS csc1 ON client_service_contact_1 = csc1.username JOIN users AS csc2 ON client_service_contact_2 = csc2.username JOIN users AS cbc ON client_business_contact = cbc.username WHERE contracts.id = ? 

Sadly, using joins is almost as verbose as using the subselects, but I assume it might be faster?

Answer 1

SELECT contracts.field1, contracts.field2,  sp1.first_name, sp1.last_name  sp2.first_name, sp2.last_name, /* etc, etc */ FROM contracts INNER JOIN users sp1 ON contracts.id = sp1.id AND sp1.username = service_provider_1 INNER JOIN  users sp2 ON contracts.id = sp2.id AND sp2.username = service_provider_2 INNER JOIN  users sobc ON contracts.id = sobc.id AND sobc.username = service_org_business_contact INNER JOIN /* etc, etc */ WHERE contracts.id = @myid 

did you also want to combine first_name and last_name for each username? You can do this like

RTRIM(sp1.first_name) + ' ' + RTRIM(sp1.last_name) as sp1_name 

in your SELECT clause. The RTRIM are necessary if the data type is (N)CHAR, not necessary if the type is (N)VARCHAR

EDIT: As stated in the comments on this answer, the JOIN on id is probably not necessary, in which case it becomes

SELECT  contracts.field1,  contracts.field2,  sp1.first_name, sp1.last_name  sp2.first_name, sp2.last_name, /* etc, etc */ FROM contracts INNER JOIN users sp1 ON sp1.username = service_provider_1 INNER JOIN  users sp2 ON sp2.username = service_provider_2 INNER JOIN  users sobc ON  sobc.username = service_org_business_contact INNER JOIN /* etc, etc */ WHERE contracts.id = @myid 

My layout probably makes it appear longer! You may need to use LEFT OUTER JOINS if it is possible to have a contract record that doesn’t have a first_name and last_name for one of it’s fields within the users table.