Question

我想要一列用于统计交易的列，其中itemtype包含两个指定值之一或location包含两个指定值之一。前两列（项目类型和位置）给出了正确的数字，但第三列似乎计算了所有交易，与项目类型或位置无关。我在做什么错了？

python -V
Python 3.6.7

which python
/usr/bin/python

Answer 1

对于最后一个，您可以使用SUM代替COUNT，如下所示-

SELECT 
  COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 END) 'itemtype',
  COUNT(CASE WHEN location IN ('Lattlast','Appelhyllan') THEN 1 END) 'location',
  sum(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 
  WHEN location IN ('Lattlast','Appelhyllan') THEN 1  
 END) 'total'  

FROM statistics

Answer 2

您不需要添加ELSE部分：

SELECT COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 END) AS itemtype,
       COUNT(CASE WHEN location IN ('Lattlast','Appelhyllan') THEN 1 END) AS location,
       COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 
                  WHEN location IN ('Lattlast','Appelhyllan') THEN 1  
             END) AS total
FROM statistics;

Answer 3

我认为，第三个条件如下

SELECT
COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') OR location IN ('Lattlast','Appelhyllan') THEN 1 END) AS total
FROM statistics;

Answer 4

COUNT不计算空值，这意味着它也从0部分“计算” ELSE。完全删除ELSE部分：

SELECT 
  COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 END) 'itemtype',
  COUNT(CASE WHEN location IN ('Lattlast','Appelhyllan') THEN 1 END) 'location',
  COUNT(CASE WHEN itemtype IN ('BARNTAL','STORSTIL') THEN 1 
             WHEN location IN ('Lattlast','Appelhyllan') THEN 1
        END) 'total'  
FROM statistics

SQL选择计数有多种情况

4 个答案: