我想说的是，您希望将null显示为空值，因此，您需要重建查询，如下所示：

CASE sm.state 
          WHEN 'null' THEN ''  AS state 
          ELSE stdd.state_name AS state 
                                  end,

改写为：

CASE  
          WHEN sm.state IS NULL THEN ''  
          ELSE stdd.state_name END AS state,

所有的“null”也是一样的。此外，应在案件结束后写上as
复习：刚刚意识到下面的句子应该是相同的，但要简洁得多，更容易阅读：

ISNULL(sm.state, '') AS state,

你可以改变主意 case 语句，它将检查 null 和空白值

case ISNULL(SM.[state],'') when '' then '' else STDD.state_name end as [state],
       case ISNULL(SM.city,'') when '' then '' else CDD.city_name end as city,
       case ISNULL(SM.country,'') when '' then '' else CD.country_name end as country

你应该使用 join 用于在select语句中提供不同表之间的where条件。或者，您可以使用下面修改过的查询

select SM.subscriber_name as name ,
       SM.accountType as accountType,
       SM.middlename as middleName,
       SM.lastname as lastName,
       SM.title as title,
       SM.email as email,
       SM.company as company,
       SM.email1 as aEmail,       
       SM.zipcode as zipcode,
       SM.phone_no as phoneNumber,
       SM.landlinenumber as landlineNumber,
       SM.login_id as loginId, 
       SD.subscriberType as subscriptionType,
       SD.product_id as productType,
       case ISNULL(SM.[state],'') when '' then '' else STDD.state_name end as [state],
       case ISNULL(SM.city,'') when '' then '' else CDD.city_name end as city,
       case ISNULL(SM.country,'') when '' then '' else CD.country_name end as country,
       SD.fulldownloadaccess as fullDownloadAccess,
       SD.emailid_limit as emailLimit,
       SD.acessTime as planTime
from subscriber_master SM, 
     subsciber_details SD,
     city_details CDD,
     state_details STDD, 
     country_details CD      
where SM.subscriber_id=16704
 and  SM.subscriber_id=SD.subscriber_id and 
      SM.country = CD.country_id and
      SM.[state] = STDD.state_id and
      SM.city = CDD.city_id;

你的查询有几个问题。首先是你的 CASE 如果表达式编写不正确，则表达式必须完整才能执行任何操作 AS 例如，

case SM.state when 'null' then '' as state else STDD.state_name as state end,

应写为

case SM.state when 'null' then '' else STDD.state_name end as state,

另外，如果您正在检查 NULL 值，而不是字符串值 'null' ，您需要编写 CASE 表达式为：

case when SM.state IS NULL then '' else STDD.state_name end as state

你还有一个额外的 , （双方 SM.email1 as aEmail, 以及 SM.zipcode as zipcode, ).
然而，这些问题都不会给你的消息在你的标题，有一些代码你没有给我们看？