根據連接表內的其他值選擇值SQL

Question

我想請求幫助提供兩個表中的值的SQL請求。

作爲一個例子，我有一個Table orders和一個表格處理。

我想報告訂單和處理狀態。

table orders 

id | status | div 
------------------- 
1 | wating_r | div1 
2 | closed | div2 
3 | closed | div3 

-

table processing: 

id | order_id | type   | date 
---------------------------------------- 
1 | 2  | send_request | 15.01.15 
2 | 2  | send_invoice | 30.01.15 
3 | 1  | send_request | 01.02.15 
4 | 3  | send_request2 | 10.02.15 
5 | 3  | send_invoice | 15.02.15 

我想得到什麼：

order_id | status | date_request | date_request2 | date_invoice 
-------------------------------------------------------------------------------- 
1  | waiting_r | 01.02.15  | NULL   | NULL 
2  | closed | 15.01.15  | NULL   | 30.01.15 
3  | closed | NULL   | 10.02.15  | 15.02.15 

我的解決方案：

select orders.id as order_id, orders.status, IF(processing.type='send_invoice',date_format(processing.date, '%Y-%m-%d'), NULL) as date_invoice, IF(processing.type='send_request',date_format(processing.date, '%Y-%m-%d'), NULL) as date_request, IF(processing.type='send_request2',date_format(processing.date, '%Y-%m-%d'), NULL) as date_request2

from orders inner join processing on orders.id = processing.order_id

where case when orders.status='closed' then processing.type='send_invoice' when orders.status='waiting_r' then processing.type='send_request' when orders.status='waiting_2'then processing.type='send_request2' end

這工作得很好，但這個IF語句我不會成爲從請求日期時，發票被送往 - 我只得到發票的日期。

而不是案件請求，我嘗試了以下，但在這種情況下，我爲每個訂單有多個行。當我嘗試「分組」時，我混合了數據。

where processing.type in ('send_invoice', 'send_request', 'completion_request_send')

Answer 1

你需要第二臺左加入到第一三倍，像這樣。與ID匹配標準與特定類型的選擇翻出你需要爲每列行

SELECT o.id AS order_id, o.status, 
     p1.date AS date_request, 
     p2.date AS date_request2, 
     p3.date AS date_invoice 
    FROM orders o 
    LEFT JOIN processing p1 ON o.id = p1.order_id AND p1.type='send_request'   
    LEFT JOIN processing p2 ON o.id = p2.order_id AND p2.type='send_request2' 
    LEFT JOIN processing p3 ON o.id = p3.order_id AND p3.type='send_invoice' 
ORDER BY 1,2 

該左聯接。與inner相反，left與join相連，允許缺少的值顯示爲null。

這是工作。 http://sqlfiddle.com/#!9/b8c74/5/0

這是加入密鑰/值表（ID /密鑰）對唯一的典型模式。

編輯不幸的是，在特定值存在重複鍵的情況下，它會生成重複的結果集行。爲了解決這個問題，在這種情況下，有必要對鍵/值表（processing）進行重複數據刪除。

此子查詢將採用最新的日期值。

   SELECT type, order_id, MAX(date) AS date 
       FROM processing 
       GROUP BY type, order_id 

然後，您必須在主查詢中使用該子查詢。如果MySQL具有公共表表達式，這將是一個好的選擇。但事實並非如此。

SELECT o.id AS order_id, o.status, 
     p1.date AS date_request, 
     p2.date AS date_request2, 
     p3.date AS date_invoice 
    FROM orders o 
    LEFT JOIN (
       SELECT type, order_id, MAX(date) AS date 
       FROM processing 
       GROUP BY type, order_id 
      ) p1 ON o.id = p1.order_id AND p1.type='send_request'   
    LEFT JOIN (
       SELECT type, order_id, MAX(date) AS date 
       FROM processing 
       GROUP BY type, order_id 
      ) p2 ON o.id = p2.order_id AND p2.type='send_request2' 
    LEFT JOIN (
       SELECT type, order_id, MAX(date) AS date 
       FROM processing 
       GROUP BY type, order_id 
      ) p3 ON o.id = p3.order_id AND p3.type='send_invoice' 
ORDER BY 1,2