有兩個條件的MySQL交叉表聚合

Question

我有一個查詢創建一個交叉表。結果是txn_id對於branda的計數，對於brandb的計數爲txn_id。

txn_id不是唯一的。這是事務表.:的一例

txn_id | nationality_id | sku | sales | units 

1  |  1   | 1 | 20 | 2 
1  |  1   | 2 | 15 | 1 
2  |  4   | 1 | 20 | 2 
3  |  2   | 1 | 10 | 1 
4  |  3   | 2 | 15 | 1 
5  |  4   | 1 | 10 | 1 

有2個其它表(products) - (sku, brand, product name)，和(nationalities) - (nationality_id, nationality)。

我想補充的第三列這讓我在那裏，這兩個品牌的購買

的txn_id計數輸出應該

nationality | branda | brandb | combined 

    1   | 1  | 1 | 1 
    2   | 1  | 0 | 0 
    3   | 0  | 1 | 0 
    4   | 2  | 0 | 0 

當前查詢。

SELECT 
    nationalities.nationality, 
    COUNT((CASE brand WHEN 'branda' THEN txn_id ELSE NULL END)) AS branda, 
    COUNT((CASE brand WHEN 'brandb' THEN txn_id ELSE NULL END)) AS brandb 
<I want my 3rd column here> 
FROM 
    transaction_data 
     INNER JOIN 
    products USING (sku) 
     INNER JOIN 
    nationalities USING (nationality_id) 
GROUP BY nationality 
ORDER BY branda DESC 
LIMIT 20; 

我已經嘗試使用：

COUNT((CASE brand WHEN 'brandb' OR 'brandb' THEN txn_id ELSE NULL END)) AS combined - 但是這顯然返回過多（返回品牌A或品牌B不管他們是否一起購買的）。我知道我不能使用AND，因爲顯然沒有一個單元格將會是branda和brandb。

我也嘗試過使用： COUNT((CASE brand WHEN IN('branda', 'brandb') THEN txn_id ELSE NULL END)) AS combined - 但這不是有效的語法。

我覺得我應該使用HAVING子句，但我不知道這將如何在列列表中工作。

Answer 1

我想你會需要聚集的兩個層次：

SELECT n.nationality, 
     sum(branda), sum(brandb), sum(branda * brandb) 
FROM (SELECT t.txn_id, n.nationality, 
      MAX(CASE brand WHEN 'branda' THEN 1 ELSE 0 END) AS branda, 
      MAX(CASE brand WHEN 'brandb' THEN 1 ELSE 0 END) AS brandb 
     FROM transaction_data t INNER JOIN 
      products p 
      USING (sku) INNER JOIN 
      nationalities n 
      USING (nationality_id) 
     GROUP BY t.txn_id, n.nationality 
    ) tn 
GROUP BY n.nationality 
ORDER BY max(txn_id) DESC 
LIMIT 20;