Sum（Case when）導致選擇的多行

Question

我有一個巨大的客戶訂單表，我想運行一個查詢來按'user_id'在過去13個月中按月列出訂單。我現在擁有的（下面）工作，但不是每user_id只列出一行，它爲user_id每個訂單列出一行。例如：一位用戶在我們的生活中總共有42份訂單，所以它列出了42行中的user_id，並且每行只有一筆付款。通常我會把它放在Excel的數據透視表中，但是我超過了100萬行的限制，所以我需要它是正確的，並且沒有成功。我想讀出來看起來像這樣：

user_id | jul_12 | aug_12 |

123456 | 150.00 | 150.00 |

不是這樣的：

user_id | jul_12 | aug_12 |

123456 | 0.00 | 150.00 |

123456 | 150.00 | 0.00 |

等40多個行

SELECT ui.user_id, 
SUM(CASE WHEN date_part('year', o.time_stamp) = 2012 AND date_part('month', o.time_stamp) = 07 THEN o.amount ELSE 0 END) jul_12, 
SUM(CASE WHEN date_part('year', o.time_stamp) = 2012 AND date_part('month', o.time_stamp) = 08 THEN o.amount ELSE 0 END) aug_12, 
FROM orders o JOIN users_info ui ON ui.user_id = o.user_id 
WHERE user_id = '123456' 
GROUP BY ui.user_id, o.time_stamp; 

Answer 1

試着這麼做：

SELECT ui.user_id, 
SUM(CASE WHEN date_part('year', o.time_stamp) = 2012 AND date_part('month', o.time_stamp) = 07 THEN o.amount ELSE 0 END) jul_12, 
SUM(CASE WHEN date_part('year', o.time_stamp) = 2012 AND date_part('month', o.time_stamp) = 08 THEN o.amount ELSE 0 END) aug_12, 
FROM orders o JOIN users_info ui ON ui.user_id = o.user_id 
WHERE user_id = '123456' 
GROUP BY ui.user_id; 

你是每個訂單獲取一條記錄，因爲你被o.time_stamp分組和時間戳對於每個順序不同。

一個較短的版本查詢：

SELECT ui.user_id, 
SUM(CASE WHEN date_trunc('month', o.time_stamp) = to_date('2012 07','YYYY MM') THEN o.amount END) jul_12, 
SUM(CASE WHEN date_trunc('month', o.time_stamp) = to_date('2012 08','YYYY MM') THEN o.amount END) aug_12, 
FROM orders o 
JOIN users_info ui ON ui.user_id = o.user_id 
WHERE ui.user_id = '123456' 
GROUP BY ui.user_id;