TSQL Counting Nulls - 所有分组项都有 NULL 字段

Question

只是想了解所需的逻辑/命令：

我有一个联系人表。每个联系人都有一个多对一的客户。 我正在尝试获取所有联系人的电子邮件都为 NULL 值的任何 clientID。

示例数据：

ContactID   EmailAddress    ClientID
1           NULL                3
907         NULL                3
2468        NULL                3
2469        email@email.com     4
1077        NULL                4
908         email@email.com     4
2           email@email.com     4
3           email@email.com     5
909         email@email.com     5

谢谢！

Answer 1

请尝试：

SELECT 
    ClientID
FROM(
    SELECT 
        ClientID, 
        SUM(CASE WHEN EmailAddress IS NULL THEN 1 ELSE 0 END) a,
        COUNT(*) b
    FROM YourTable
    GROUP BY ClientID
)x WHERE a=b

Answer 2

您可以使用分组聚合和HAVING 子句来做到这一点（假设空白电子邮件地址可以被视为空值）：

SELECT 
    ClientID
    FROM ClientEmails
    GROUP BY ClientID
    HAVING MAX(LEN(ISNULL(EmailAddress, ''))) = 0;

SqlFiddle

Answer 3

这会有帮助吗？

select *
from
(
select clientId, 
COUNT(emailAddress) as Mailz, 
COUNT(contactId) as Contacts
from contacts
group by clientId
) as src
where (Mailz = 0 and contacts > 0)