Question

我有以下查询来返回客户使用的作业（访问次数）以及他/她使用的独特审核。

SELECT 
customer.users_id AS CustID, 
COUNT(VisitID) AS Jobs, 
COUNT(DISTINCT VetID) AS Resources 
FROM customer 
LEFT JOIN visit ON customer.users_id = visit.CustID 
GROUP BY customer.users_id

当我添加WHERE子句以仅计算未重新计划或已取消的访问次数时，我的查询如下所示。

SELECT 
customer.users_id AS CustID, 
COUNT(VisitID) AS Jobs, 
COUNT(DISTINCT VetID) AS Resources 
FROM customer LEFT JOIN visit ON customer.users_id = visit.CustID 
WHERE visit.Status != 'Cancelled' AND visit.Status != 'ReScheduled' 
GROUP BY customer.users_id

但是，在这种情况下，我只会收到没有取消或重新安排访问的客户，虽然我正在为客户使用左连接，但我才知道。

我如何适应WHERE子句呢？

Answer 1

您不需要WHERE子句。这只会将LEFT JOIN变为INNER JOIN。您需要AND上的LEFT JOIN：

SELECT customer.users_id AS CustID, COUNT(VisitID) AS Jobs, COUNT(DISTINCT     VetID) AS Resources 
FROM customer 
LEFT JOIN visit ON customer.users_id = visit.CustID 
AND visit.Status NOT IN('Cancelled','ReScheduled')
GROUP BY customer.users_id

Answer 2

当我们使用Format添加where子句时，它的行为类似于DateTimePickerFormat.Custom，其中过滤器应用于left outer join子句之后。用inner join子句

替换ON后尝试

where

SQL JOIN

2 个答案: