如何在select中過濾空值？

Question

我有一個表：

DataTable: 
id int, 
user_id int, 
field_id int, 
value varchar 

DataExample：

id user_id field_id value 
1  1   1  'Peter' 
2  1   2  56 
3  1   3  100 
4  2   1  'Buzz' 
5  2   2  47 
6  2   3  120 
7  3   1  'Wolf' 
8  3   2  null 
9  3   3  null 

我想field_id財產來分隔值列：

Name Age  Score 
Peter 56  100 
Buzz 47  120 

我做的：

SELECT id, MAX(Name) AS Name, MAX(Age) AS Age, MAX(Score) AS Score 
FROM (
SELECT u.id 
CASE 
    WHEN field_id = 1 THEN value 
END as Name, 
CASE 
    WHEN field_id = 2 THEN value 
END as Age, 
CASE 
    WHEN field_id = 3 THEN value 
END as Score 
FROM Users u 
INNER JOIN DataTable t ON (t.user_id=u.id) 
) AS sub 
GROUP BY id; 

這是很好的作品。但現在我想過濾空值。我的意思是我不想選擇Age或Score = null。我嘗試在CASE塊中添加is not null，但它沒有幫助。
任何建議？

Answer 1

做一個雙自聯接：

select t1.value as name, t2.value as Age, t3.value as Score 
from (select userid, value from DataTable where field_id = 1) as t1 
join (select userid, value from DataTable where field_id = 2) as t2 ON t1.userid = t2.userid 
join (select userid, value from DataTable where field_id = 3) as t3 ON t1.userid = t3.userid 

第一個子查詢返回的名字，第二個返回年齡和第三得分。

Answer 2

SELECT id, MAX(Name) AS Name, MAX(Age) AS Age, MAX(Score) AS Score 
FROM (
SELECT u.id 
CASE 
    WHEN field_id = 1 THEN value 
END as Name, 
CASE 
    WHEN field_id = 2 THEN value 
END as Age, 
CASE 
    WHEN field_id = 3 THEN value 
END as Score 
FROM Users u 
INNER JOIN DataTable t ON (t.user_id=u.id) 
    WHERE value IS NOT NULL -------------------here 
) AS sub 
GROUP BY id;