collesce問題與mysql

Question

我有一個漂亮的平坦表 - tbl_values其中有userids以及netAmounts在給定的行。在以下示例中，根據時間戳，2280在過去30天內沒有記錄。

我希望這會返回3行，2280爲「0」 - 但我只得到2回？我在這裏錯過了很明顯的東西嗎

SELECT userid, (COALESCE(SUM(netAmount),0)) as Sum FROM `tbl_values` where userid in (2280, 399, 2282) and date > (select DATE_SUB(NOW(), INTERVAL 30 day)) GROUP BY userid 

Answer 1

假設你總是希望返回用戶，不管他們寧可在tbl_values匹配的記錄，你要找什麼是outer join：

SELECT u.userid, COALESCE(SUM(v.netAmount),0) as Sum 
FROM (
    SELECT 2280 userid UNION ALL 
    SELECT 399 UNION ALL 
    SELECT 2282 
) u 
    LEFT JOIN `tbl_values` v ON u.userid = v.userid AND 
     v.date > DATE_SUB(NOW(), INTERVAL 30 day) 
GROUP BY u.userid 

---

如果你也許有一個Users表，那麼你可以用它代替子查詢。

SELECT u.userid, COALESCE(SUM(v.netAmount),0) as Sum 
FROM users u 
    LEFT JOIN `tbl_values` v ON u.userid = v.userid AND 
     v.date > DATE_SUB(NOW(), INTERVAL 30 day) 
WHERE u.userid in (2280, 399, 2282) 
GROUP BY u.userid 

Answer 2

這是您的查詢：

SELECT userid, (COALESCE(SUM(netAmount),0)) as Sum 
FROM `tbl_values` 
where userid in (2280, 399, 2282) and 
     date > (select DATE_SUB(NOW(), INTERVAL 30 day)) 
GROUP BY userid; 

的where子句中的過濾器找到匹配的用戶ID 2280是假設至少有一行的某處存在任何行，你可以得到你想要的東西通過移動date比較條件聚合：

SELECT userid, 
     sum(case when date > DATE_SUB(NOW(), INTERVAL 30 day) 
       then netAmount else 0 
      end) as Sum 
FROM `tbl_values` 
WHERE userid in (2280, 399, 2282) 
GROUP BY userid; 

編輯：

如果你真的希望所有的三個結果，然後用left join：

SELECT u.userid, 
     coalesce(sum(netAmount), 0) as Sum 
FROM (select 2280 as userid union all 
     select 399 union all 
     select 2282 
    ) u left join 
     tbl_values t 
     on u.userid = t.userid and 
     t.date > DATE_SUB(NOW(), INTERVAL 30 day) 
GROUP BY u.userid;