SQL联合查询左表中不匹配的行

Question

我有两个表，sfuser和membership

sfuser获得139，会员表获得50

我需要查询来选择谁不是任何项目的成员，这意味着89个成员

这是我的查询

select sfuser.id,sfuser.username,sfuser.email from sfuser INNER JOIN projectmembership ON sfuser.id = projectmembership.member_id ;

但是我正想获得50个成员用户，反之

请丢点光

最好的问候Sathish

Answer 1

select 
sfuser.id,
sfuser.username,
sfuser.email 
from sfuser 
LEFT JOIN projectmembership ON sfuser.id = projectmembership.member_id
WHERE 
projectmembership.member_id is NULL

它应该返回不在projectmembership表中的所有用户。

Answer 2

INNER JOIN将只产生与两个表都匹配的行。您可以进行左联接并过滤出空白记录。 就像是：

SELECT sfuser.id,
sfuser.username,
sfuser.email
FROM sfuser LEFT JOIN projectmembership ON sfuser.id = projectmembership.member_id
WHERE (projectmembership.member_id is null);

Answer 3

内部联接将返回在两个表之间共享进行联接的值的所有行。 （参见此图 ）

您要查找的是左连接，即左表中所有不匹配的行。

select sfuser.id,
  sfuser.username,
  sfuser.email 
from sfuser 
LEFT JOIN projectmembership 
  ON sfuser.id = projectmembership.member_id

Answer 4

如果sfuser记录在项目成员资格表中可以多次出现，那么请忘记外部联接-NOT EXISTS是您想要的：

select sid,
       username,
       email
from   sfuser
where  not exists (
         select null
         from   projectmembership
         where  sfuser.id = projectmembership.member_id);