[英]How to select rows with WHERE statement and COUNT(*) = 1
我正在嘗試將WHERE
子句與HAVING COUNT(*)
子句結合起來。 但我無法得到我想要的結果。
我想找到所有只下過一個訂單並且訂單是"inactive"
。 換句話說,我試圖從 customer_name 值的計數為 "1" 並且訂單狀態等於"inactive"
的訂單表中選擇行。
我有這張桌子:
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 |
+----+--------------+-------------+---------+-------+
我想要每個只有一個訂單的客戶的名字,並且訂單是“非活動”的。 從上表中,我想要這些結果:
+----+--------------+-------------+---------+-------+
| 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 |
+----+--------------+-------------+---------+-------+
我嘗試了這個查詢,以及使用 WHERE 和 COUNT() 的許多變體:
SELECT ID, cust_name, status, item_no, price, COUNT(*)
FROM orders_tbl
WHERE status = 'inactive'
GROUP BY cust_name
HAVING COUNT(*)<2;
上面的查詢產生了接近我想要的結果。 但是我得到的客戶有一個"inactive"
記錄,即使他們有一個或多個活動記錄。 我得到的結果是:
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 |
+----+--------------+-------------+---------+-------+
一種解決方案是使用聚合,並將邏輯移動到HAVING
子句。以下查詢可以為您提供滿足條件的客戶名稱::
SELECT cust_name
FROM mytable
GROUP BY cust_name
HAVING COUNT(*) = 1 AND MAX(status) = 'inactive'
回報:
| cust_name |
| --------- |
| Earl |
| Eric |
| Jenny |
如果您還想查看訂單,則可以將其轉換為子查詢:
SELECT *
FROM mytable
WHERE cust_name IN (
SELECT cust_name
FROM mytable
GROUP BY cust_name
HAVING COUNT(*) = 1 AND MAX(status) = 'inactive'
)
結果 :
| ID | cust_name | status | item_no | price |
| --- | --------- | -------- | ------- | ----- |
| 3 | Eric | inactive | 3 | 8 |
| 6 | Earl | inactive | 1 | 5 |
| 9 | Jenny | inactive | 4 | 8 |
從 MySQL 8.0 開始,窗口函數使它變得更容易、更高效。 您可以內聯它們以計算客戶的訂單總數,以及非活動訂單的數量; 然后在兩個值都為1
記錄中進行擬合:
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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