[英]How to select rows with WHERE statement and COUNT(*) = 1
我正在尝试将WHERE
子句与HAVING COUNT(*)
子句结合起来。 但我无法得到我想要的结果。
我想找到所有只下过一个订单并且订单是"inactive"
。 换句话说,我试图从 customer_name 值的计数为 "1" 并且订单状态等于"inactive"
的订单表中选择行。
我有这张桌子:
orders_tbl
+----+--------------+-------------+---------+-------+
| ID | cust_name | status | item_no | price |
+----+--------------+-------------+---------+-------+
| 1 | Scott | active | 4 | 2.0 |
+----+--------------+-------------+---------+-------+
| 2 | James | active | 2 | 4.0 |
+----+--------------+-------------+---------+-------+
| 3 | Eric | inactive | 3 | 8.0 |
+----+--------------+-------------+---------+-------+
| 4 | Polly | active | 3 | 2.0 |
+----+--------------+-------------+---------+-------+
| 5 | Peggy | inactive | 6 | 4.0 |
+----+--------------+-------------+---------+-------+
| 6 | Earl | inactive | 1 | 5.0 |
+----+--------------+-------------+---------+-------+
| 7 | Billy | active | 4 | 2.0 |
+----+--------------+-------------+---------+-------+
| 8 | Peggy | inactive | 5 | 4.0 |
+----+--------------+-------------+---------+-------+
| 9 | Jenny | inactive | 4 | 8.0 |
+----+--------------+-------------+---------+-------+
| 10 | Polly | active | 2 | 2.0 |
+----+--------------+-------------+---------+-------+
| 11 | Scott | inactive | 2 | 4.0 |
+----+--------------+-------------+---------+-------+
| 12 | James | inactive | 1 | 8.0 |
+----+--------------+-------------+---------+-------+
我想要每个只有一个订单的客户的名字,并且订单是“非活动”的。 从上表中,我想要这些结果:
+----+--------------+-------------+---------+-------+
| ID | cust_name | status | item_no | price |
+----+--------------+-------------+---------+-------+
| 3 | Eric | inactive | 3 | 8.0 |
+----+--------------+-------------+---------+-------+
| 6 | Earl | inactive | 1 | 5.0 |
+----+--------------+-------------+---------+-------+
| 9 | Jenny | inactive | 4 | 8.0 |
+----+--------------+-------------+---------+-------+
我尝试了这个查询,以及使用 WHERE 和 COUNT() 的许多变体:
SELECT ID, cust_name, status, item_no, price, COUNT(*)
FROM orders_tbl
WHERE status = 'inactive'
GROUP BY cust_name
HAVING COUNT(*)<2;
上面的查询产生了接近我想要的结果。 但是我得到的客户有一个"inactive"
记录,即使他们有一个或多个活动记录。 我得到的结果是:
orders_tbl
+----+--------------+-------------+---------+-------+
| ID | cust_name | status | item_no | price |
+----+--------------+-------------+---------+-------+
| 3 | Eric | inactive | 3 | 8.0 |
+----+--------------+-------------+---------+-------+
| 5 | Peggy | inactive | 6 | 4.0 |
+----+--------------+-------------+---------+-------+
| 6 | Earl | inactive | 1 | 5.0 |
+----+--------------+-------------+---------+-------+
| 9 | Jenny | inactive | 4 | 8.0 |
+----+--------------+-------------+---------+-------+
| 11 | Scott | inactive | 2 | 4.0 |
+----+--------------+-------------+---------+-------+
| 12 | James | inactive | 1 | 8.0 |
+----+--------------+-------------+---------+-------+
一种解决方案是使用聚合,并将逻辑移动到HAVING
子句。以下查询可以为您提供满足条件的客户名称::
SELECT cust_name
FROM mytable
GROUP BY cust_name
HAVING COUNT(*) = 1 AND MAX(status) = 'inactive'
回报:
| cust_name |
| --------- |
| Earl |
| Eric |
| Jenny |
如果您还想查看订单,则可以将其转换为子查询:
SELECT *
FROM mytable
WHERE cust_name IN (
SELECT cust_name
FROM mytable
GROUP BY cust_name
HAVING COUNT(*) = 1 AND MAX(status) = 'inactive'
)
结果 :
| ID | cust_name | status | item_no | price |
| --- | --------- | -------- | ------- | ----- |
| 3 | Eric | inactive | 3 | 8 |
| 6 | Earl | inactive | 1 | 5 |
| 9 | Jenny | inactive | 4 | 8 |
从 MySQL 8.0 开始,窗口函数使它变得更容易、更高效。 您可以内联它们以计算客户的订单总数,以及非活动订单的数量; 然后在两个值都为1
记录中进行拟合:
SELECT * FROM (
SELECT
t.*,
COUNT(*) OVER(PARTITION BY cust_name) cnt_total,
SUM(status = 'inactive') OVER(PARTITION BY cust_name) cnt_inactive
FROM mytable t
) x WHERE cnt_total = 1 AND cnt_inactive = 1;
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