mysql - 带有 IN 语句的 IFNULL 与 mysql

Question

我是 mysql 的新手....它可能看起来很麻烦....但我已经尝试了 3 个小时...这是我正在尝试做的......

SELECT
  MERCHANT_ID,
  IFNULL(COUNT(SUBSCRIBE_ID),0)
FROM SUBSCRIBE_TABLE
WHERE
  MERCHANT_ID IS NULL OR 
  MERCHANT_ID IN(1000000000066,1000000000104,1000000000103,1000000000105)
GROUP BY MERCHANT_ID
ORDER BY
  FIND_IN_SET(MERCHANT_ID,'1000000000066,1000000000104,1000000000103,1000000000105');

输出是...

+------------------+---------------------------------+
| MERCHANT_ID      |   IFNULL(COUNT(SUBSCRIBE_ID),0) |
+------------------+---------------------------------+
|    1000000000066 |                               2 |
|    1000000000103 |                               1 |
+------------------+---------------------------------+

但我期待以下列方式...

+------------------+---------------------------------+
| MERCHANT_ID      |   IFNULL(COUNT(SUBSCRIBE_ID),0) |
+------------------+---------------------------------+
|    1000000000066 |                               2 |
|    1000000000104 |                               0 |
|    1000000000103 |                               1 |
|    1000000000105 |                               0 |
+------------------+---------------------------------+

我尝试添加 MERCHANT_ID IS NULL...但无法使用默认值获得结果...:(

Answer 1

您只会获得实际在 SUBSCRIBE_TABLE 中的记录。如果您想获取所有 ID 的记录，则必须首先使用这些值“创建一个临时表”(或在这种情况下使用带有 UNION 的子查询)，然后将结果加入其中.

您的查询可能如下所示:

SELECT
  merchant_id,
  COUNT(subscribe_id)
FROM
  (SELECT 1000000000066 AS merchant_id, 1 AS SortKey
   UNION ALL
   SELECT 1000000000104 AS merchant_id, 2 AS SortKey
   UNION ALL
   SELECT 1000000000103 AS merchant_id, 3 AS SortKey
   UNION ALL
   SELECT 1000000000105 AS merchant_id, 4 AS SortKey
  ) AS temp
LEFT JOIN subscribe_table USING (merchant_id)
GROUP BY merchant_id
ORDER BY SortKey ASC

我用子查询中的列 SortKey 替换了您的 FIND_IN_SET。 COUNT 将只计算非空行，如果没有找到则返回 0。您不需要围绕它的 IFNULL。

如果您有超过 4 个 merchant_id，您可能需要考虑使用临时表做同样的事情。有关示例，请参见此处:
Mysql: Create inline table within select statement?