代码之家 › 专栏 › 技术社区 › iLemming

空字段的ISNULL等效值

isnull coalesce sql-server-2005 sql

2

iLemming · 技术社区 · 15 年前

是否有类似ISNULL()或COALESCE()的东西,但不是检查null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

ISNULL和COALESCE在这里不起作用我不知道为什么

3 回复 | 直到 15 年前

1

8

Andomar 15 年前

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

2

3

KM. 15 年前

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

3

1

Nathan Wheeler 15 年前

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