具有2个条件的MySQL交叉表聚合

我有一个创建交叉表的查询.结果是branda的txn_id计数,以及brandb的txn​​_id计数.

txn_id不是唯一的.这是交易表的一个例子：

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

还有2个表(产品) – (sku,品牌,产品名称)和(国籍) – (nationality_id,国籍).

我想添加第三列,让我获得购买BOTH品牌的txn_id数量

输出应该是

nationality | branda | brandb | combined

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

当前查询.

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;

我尝试过使用：

COUNT((CASE品牌WHEN’brandb’OR’brandb’THEN txn_id ELSE NULL END))AS结合 – 但这显然会返回太多(无论是否一起购买,都会返回branda或brandb).我知道我不能使用AND,因为很明显没有一个单元格将成为branda和brandb.

我也试过用：
COUNT((CASE品牌WHEN IN(‘branda’,’brandb’)THEN txn_id ELSE NULL END))AS组合 – 但这不是有效的语法.

我觉得我应该使用HAVING子句,但我不确定这在列列表中是如何工作的.

解决方法:

我认为你需要两个级别的聚合：

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;

标签：mysql,sql,crosstab
来源： https://codeday.me/bug/20190711/1432058.html