不同的SELECT和VIEW中的SELECT结果

Question

SELECT语句的结果与VIEW中的SELECT结果不同。如何解决问题并从视野中获得相同的结果？

动作表：

+--+---------+--------------+-----------+------+ 
|id|person_id|action_type_id|currency_id|sum | 
+--+---------+--------------+-----------+------+ 
|1 |1  |1    |1   | 1.00 | 
|2 |1  |1    |1   | 5.00 | 
|3 |1  |1    |2   |10.00 | 
|4 |1  |2    |1   | 2.00 | 
|5 |2  |1    |1   |20.00 | 
|6 |2  |2    |2   | 5.00 | 
+--+---------+--------------+-----------+------+ 

选择：

SELECT person_id AS p, currency_id AS c, 
(
CAST(
COALESCE(
(SELECT SUM(sum) FROM actions WHERE action_type_id=1 AND person_id=p AND currency_id=c) 
, 0) 
AS DECIMAL(11,2)) - 
CAST(
COALESCE(
(SELECT SUM(sum) FROM actions WHERE action_type_id=2 AND person_id=p AND currency_id=c) 
, 0) 
AS DECIMAL(11,2)) 
) AS sum 
FROM actions 
GROUP BY currency_id, person_id 
ORDER BY person_id, currency_id; 

结果：

+--+--+------+ 
|p |c |sum | 
+--+--+------+ 
|1 |1 | 4.00 | 
|1 |2 |10.00 | 
|2 |1 |20.00 | 
|2 |2 |-5.00 | 
+--+--+------+ 

选择内部视图：

CREATE VIEW p_sums AS 
SELECT person_id AS p, currency_id AS c, 
(
CAST(
COALESCE(
(SELECT SUM(sum) FROM actions WHERE action_type_id=1 AND person_id=p AND currency_id=c) 
, 0) 
AS DECIMAL(11,2)) - 
CAST(
COALESCE(
(SELECT SUM(sum) FROM actions WHERE action_type_id=2 AND person_id=p AND currency_id=c) 
, 0) 
AS DECIMAL(11,2)) 
) AS sum 
FROM actions 
GROUP BY currency_id, person_id 
ORDER BY person_id, currency_id; 

SELECT * FROM p_sums; 

结果：

+--+--+------+ 
|p |c |sum | 
+--+--+------+ 
|1 |1 |29.00 | 
|1 |2 |29.00 | 
|2 |1 |29.00 | 
|2 |2 |29.00 | 
+--+--+------+ 

Answer 1

你能不能做：

SELECT person_id AS p, currency_id AS c, SUM(CASE action_Type_id WHEN 1 THEN sum WHEN 2 THEN -sum END) as sum 
FROM actions 
GROUP BY currency_id, person_id 
ORDER BY person_id, currency_id; 

即摆脱子查询，并建立一个单一的总结（使action_type_id 2值为负）