Question

是否存在类似ISNULL（）或COALESCE（）的内容，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

而不是返回四列我想要得到三个而第三个假设有cu.email或hu.email的值，如果第一个是EMPTY！ ISNULL和COALESCE不在这里工作我不知道为什么

Answer 1

您可以随时使用案例：

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

Answer 2

查看NULLIF (Transact-SQL)

NULLIF返回第一个表达式if 这两个表达方式并不相同。如果表达式是相等的，NULLIF 返回类型为null的null值第一个表达。

试试这个：

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

如果cu.email和hu.email是空字符串或NULL

的任意组合，

将返回NULL

Answer 3

这将捕获null或空cu.email并改为使用hu.email：

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

ISNULL等效于空字段

3 个答案: