如何从一个查询中提取多个用​​户信息？

Question

I have an invoice table that holds the id of the user that sent the invoice ( from_id ) and the user that received the invoice ( to_id ).

I want to be able to pull both of their info from the profile table but I am unable to figure out how.

Below is the query I'm running that let's me pull info for just one user ( from_id ) because of the join.

SELECT jobs.title, profiles.display_name, invoice.to_id, invoice.from_id, invoice.amount
FROM (invoice) 
JOIN jobs ON jobs.job_id = invoice.job_id 
JOIN profiles ON invoice.from_id = profiles.user_id 
WHERE `invoice_id` = '3'

Answer 1

You can use the same table twice. Give them different aliased, which I think makes a query more readable anyway.

SELECT 
  j.title, 
  tp.display_name as to_name, fp.display_name as from_name, 
  i.to_id, i.from_id, 
  i.amount
FROM 
  invoice i
  JOIN jobs j ON j.job_id = i.job_id 
  JOIN profiles fp ON i.from_id = fp.user_id 
  JOIN profiles tp ON i.to_id = tp.user_id 
WHERE 
  i.invoice_id= '3'

Answer 2

You can join on a table more than once - in this case you need to join on the profiles table twice - once to get information about who the invoice is from and once to get the information about the user the invoice was sent to.

SELECT jobs.title
    , Profile_From.display_name AS [From]
    , Profile_To.display_name AS [To]
    , invoice.to_id
    , invoice.from_id
    , invoice.amount
FROM invoice 
JOIN jobs 
    ON jobs.job_id = invoice.job_id 
JOIN profiles Profile_From
    ON invoice.from_id = Profile_From.user_id 
-- You are just missing this part
JOIN profiles Profile_To
    ON invoice.to_id = Profile_To.user_id 
WHERE invoice_id= '3'