如何获得所有记录甚至那些没有匹配连接的记录 - MySQL

Question

I have the following SQL which is getting all of the customer records and then finding the matching documents for that customer (points_audit_customers.id = points_audit_documents._audit_id) and it works however it is skipping all customers that do not have a document to match which was fine originally but now the spec has changed and I need all customers to come though, if no document is found then still show the customer details but leave the document fields from the sql as zero or null.

Is this possible? I was wondering if somehow CASE could be used? I guess if it isn't possible I can modify the SQL to only select customer details then in the PHP loop select the matching document, ideally I would prefer to do it with the SQL statment if I can.

Thankyou

SELECT points_audit_customers.*, points_audit_documents.branch,
SUM(points_audit_documents.amount_invoiced) AS the_amount_invoiced,
SUM(points_audit_documents.amount_spent) AS the_amount_spent,    
SUM(points_audit_documents.points_invoiced) as invoiced_points,  
SUM(points_audit_documents.points_spent) as spent_points,
SUM(points_audit_documents.points_bonus) as bonus_points
FROM points_audit_customers, points_audit_documents
WHERE import_month = '$import_month'
AND points_audit_customers.id = points_audit_documents.audit_id
AND processed = 1

Answer 1

You need to use an outer join :

FROM  points_audit_customers LEFT JOIN points_audit_documents
        ON points_audit_customers.id = points_audit_documents.audit_id
WHERE import_month = '$import_month'
  AND processed = 1  -- if this is in documents table, move to the join criteria

Answer 2

SELECT pac.*, pad.branch,
    IFNULL(SUM(pad.amount_invoiced), 0) AS the_amount_invoiced,
    IFNULL(SUM(pad.amount_spent), 0)    AS the_amount_spent,    
    IFNULL(SUM(pad.points_invoiced), 0) AS invoiced_points,  
    IFNULL(SUM(pad.points_spent), 0)    AS spent_points,
    IFNULL(SUM(pad.points_bonus), 0)    AS bonus_points
FROM points_audit_customers pac 
LEFT JOIN points_audit_documents pad ON ( pad.id = pac.audit_id )
WHERE processed = 1
    AND import_month = '$import_month'
GROUP BY pac.id