高级MySQL左加入IFNULL查询

Question

我正在寻求有关高级 MySQL 查询的帮助。我当前的查询（如下所示）工作正常。我想添加一个额外的字段，这样我就不必创建单独的查询。新字段 count(TableA.Field05) 应生成 TableA.

中的记录总数

表A有10条记录
表 B 有 100 条记录

SELECT count(TableB.Answer) AS unAnswered 
FROM TableA 
LEFT JOIN TableB 
ON ( TableA.Field01 = TableB.fkField01 AND TableA.Field02 = TableB.fkField02 AND TableB.Answer = '1') 
WHERE TableB.fkField03 IS NULL AND TableA.Field04 = 10 
GROUP BY TableA.Field01, TableA.Field02

结果：

unAnswered = 8 这是正确的

期望的结果是：

unAnswered = 8 count(TableA.Field05) = 10

--

这是数据和结果的示例。

SELECT count(TableB.Answer) AS unAnswered
FROM TableA LEFT JOIN TableB ON ( TableA.Field01 = TableB.fkField01 AND TableA.Field02 = TableB.fkField02 AND TableB.Answer = '1')
WHERE TableB.fkField03 IS NULL AND TableA.Field04 = 10
GROUP BY TableA.Field01, TableA.Field02

TableA
Field01 = 1, Field02 = 1, Field03 = 10
Field01 = 1, Field02 = 2, Field03 = 21
Field01 = 1, Field02 = 3, Field03 = 22
Field01 = 1, Field02 = 4, Field03 = 34

TableB
Field01 = 1, Field02 = 1, Answer = 1
Field01 = 1, Field02 = 2, Answer = 1
Field01 = 1, Field02 = 3, Answer = 1
Field01 = 2, Field02 = 1, Answer = 1
Field01 = 2, Field02 = 2, Answer = 1
Field01 = 2, Field02 = 3, Answer = 1

Result
count(TableB.Answer) AS unAnswered = 1


Result trying to achive
count(TableB.Answer) AS unAnswered = 1
count(TableA.Field03) = 4

任何帮助将不胜感激。

Answer 1

如果您只是想将 tableA 的计数添加到当前查询中，只需将其添加到您的 select 语句中即可：

'SELECT count(TableB.Answer) AS unAnswered, count(TableA.Field02) FROM TableA ...'

Answer 2

我刚刚想出了我自己的问题。

SELECT **COALESCE(count(DISTINCT TableB.Answer)) AS unAnswered, count(DISTINCT TableA.Field05)**
FROM TableA 
LEFT JOIN TableB 
ON ( TableA.Field01 = TableB.fkField01 AND TableA.Field02 = TableB.fkField02 AND TableB.Answer = '1') 
WHERE TableB.fkField03 IS NULL AND TableA.Field04 = 10 
GROUP BY TableA.Field01, TableA.Field02

添加 COALESCE 和 DISTINCT 解决了我的问题。谢谢大家的帮助。

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