空字段的ISNULL等效值

您可以始终使用用例:

select  case when cu.email is null or cu.email = '' then hu.email 
             else cu.email end as ColumnName
from    YourTable

看看 NULLIF (Transact-SQL)

NULLIF返回第一个表达式if 表达式相等,如果为空

试试这个:

COALESCE(NULLIF(cu.email,''),NULLIF(hu.email,''))

如果特写邮件以及hu.E邮箱是空字符串或NULL的任意组合

这将捕获null或空特写邮件使用hu.E邮箱取而代之的是:

SELECT cu.last_name, 
       cu.first_name, 
       CASE WHEN ISNULL(cu.email, '') = '' THEN
            hu.email
       ELSE
            cu.email
       END AS email
FROM 
(
  SELECT DISTINCT c.first_name, 
                  c.last_name, 
                  c.email, 
                  c.household_id, 
                  h.head_of_household_id
  FROM rd_customers c
  JOIN rd_households h 
    ON c.household_id = h.household_id
  JOIN ad_registrations r 
    ON r.customer_id = c.customer_id
  JOIN ad_meeting_times a 
    ON  r.session_id = a.session_id 
      AND a.meeting_time_id = 203731
) cu
LEFT JOIN rd_customers hu 
  ON hu.customer_id = cu.head_of_household_id