如何获取所有记录，即使那些没有匹配的连接 - MySQL

Question

我有以下SQL获取所有客户记录，然后找到该客户的匹配文档（points_audit_customers.id = points_audit_documents._audit_id），但它的工作原理它跳过所有没有文件匹配的客户，原本很好，但现在规范已经改变，我需要所有的客户来，如果没有找到文件，仍然显示客户的详细信息，但离开文件字段sql为零或null。

这可能吗？我想知道是否可以使用CASE吗？我想如果这是不可能的，我可以修改SQL来只选择客户的详细信息，然后在PHP循环中选择匹配的文档，理想情况下，如果可以的话，我宁愿用SQL语句来完成。

三江源

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

您需要使用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