sql - ISNULL 等效于空字段

Question

是否有像 ISNULL() 或 COALESCE() 这样的东西，但不是检查空值而是检查空值。

例如:

  SELECT cu.last_name, cu.first_name, cu.email, hu.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

我不想返回四列，而是想得到三列，如果第一列为空，则第三列应该具有 cu.email 或 hu.email 的值! ISNULL 和 COALESCE 在这里不起作用，我不知道为什么

Answer 1

你总是可以使用案例:

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