Question

我有两张桌子A和B

表A

ID_number as PK
first_name, 
L_Name

表B

ID_number, 
Email_id,
Flag

我有几个人拥有多个电子邮件ID，并且已在表B上标记为X.

我正在尝试查找拥有电子邮件ID或多个电子邮件ID的人员列表，但从未被标记过。

例如John clark表B中可能有2封电子邮件，但从未被标记过。

Answer 1

只需使用not exists：

select a.*
from a
where not exists (select 1 
                  from b
                  where b.id_number = a.id_number and b.flag = 'X'
                 );

Answer 2

您可能想要执行更新，但您的问题似乎只是关于选择（可能基于选择进行更新）。它应该是这样的：

SELECT A.L_Name
FROM A 
WHERE NOT EXISTS (
    SELECT 1 
    FROM B 
    WHERE B.ID_number = A.ID_number AND B.Flag = 'X'
)

OR LEFT JOIN版

SELECT 1
FROM A 
    LEFT JOIN B ON B.ID_number = A.ID_number AND B.Flag = 'X'
WHER B.ID_number IS NULL

通常，第一个版本比第二个版本快。

Answer 3

忘记表A ......

SELECT DISTINCT ID_number FROM table_b t1 
WHERE NOT EXISTS(
SELECT NULL FROM table_b t2 WHERE t1.ID_number=t2.ID_number AND t2.flag='X'
)

Answer 4

根据您在评论中的回答判断，我相信这正是您所寻找的：

--drop table update_test;

create table update_test
(
    id_num      number,
    email_id    number,
    flag        varchar2(1) default null
);

insert into update_test values (1, 1, null);
insert into update_test values (1, 2, null);
insert into update_test values (2, 3, null);
insert into update_test values (2, 7, null);
insert into update_test values (3, 2, null);
insert into update_test values (3, 3, 'X');
insert into update_test values (3, 7, null);

select * from update_test;

select id_num, min(email_id)
from update_test
group by id_num;

update update_test ut1
set flag = case 
    when email_id = (
        select min(email_id) 
        from update_test ut2 
        where ut2.id_num = ut1.id_num
    ) then 'X' 
    else null end
where id_num not in (
    select id_num 
    from update_test
    where Flag is not null);

最后一次更新语句将更新并设置Flag最低id_num的{{1}}组记录中的email_id字段。如果id_num组已将Flag字段设置为1，则会忽略它。

根据IF Else Condition更新列

4 个答案: