SELECT语句

Question

删除空字段我有一个select语句如下：

SELECT 
    firstName, 
    lastName, 
    CASE 
     WHEN primaryEmail <> 'name@example.com' THEN primaryEmail 
     WHEN secondaryEmail <> 'name@example.com' THEN secondaryEmail 
     ELSE ternaryEmail 
    END AS email 
FROM participant 
WHERE 
    primaryEmail <> 'name@example.com' 
    OR secondaryEmail <> 'name@example.com' 
    OR ternaryEmail <> 'name@example.com' 

的问题是，有一些记录与空字段，无论是名字，姓氏，或所得的电子邮件。我将此添加到WHERE子句中：

firstName IS NOT NULL 
AND lastName IS NOT NULL 
AND primaryEmail <> // The already existing WHERE clause code. 

但这些字段仍显示出来。我还没有试图摆脱电子邮件部分，所以没有代码让我在那里展示。

Answer 1

SELECT 
     firstName, 
     lastName, 
     CASE 
      WHEN primaryEmail <> 'name@example.com' THEN primaryEmail 
      WHEN secondaryEmail <> 'name@example.com' THEN secondaryEmail 
      ELSE ternaryEmail 
     END AS email 
    FROM participant 
    WHERE 
     (primaryEmail <> 'name@example.com' AND primaryEmail IS NOT NULL) OR 
     (secondaryEmail <> 'name@example.com' AND secondaryEmail IS NOT NULL) OR 
     (ternaryEmail <> 'name@example.com' AND ternaryEmail IS NOT NULL) 

Answer 2

你需要or逻辑，不and

where 
(firstName is not null or lastName is not null) 
and other conditions 

Answer 3

这个问题是一个棘手的T-SQL。我确实找到了这个问题的答案，并且确切了解了编译器如何查看空格或NULL的每个“类型”。

http://weblogs.sqlteam.com/mladenp/archive/2007/09/06/How_does_SQL_Server_really_store_NULL-s.aspx