MySQL SUM left join 显示所有类别即使总和为0

Question

我希望根据一组数据的得分总和来选择所有类别，即使该数据集不包含类别。但是，无论我尝试什么，它总是只显示具有实际数据的类别。

我创建了以下 SQLFiddle http://sqlfiddle.com/#!9/52a127/3

为了便于查看，我将在此处粘贴select 语句:

SELECT categories.id, IFNULL(SUM(raw_data.score), 0) as total
FROM categories
LEFT JOIN raw_data ON categories.id = raw_data.category_id
WHERE
(raw_data.quarter = '2018Q2' OR !raw_data.quarter) AND
raw_data.broker_id = 2 
GROUP BY categories.id
ORDER BY total DESC

正如您从 fiddle 中看到的那样，它只显示 2 个类别，但我希望选择所有 6 个类别，并为没有结果的类别设置 0。

感谢任何帮助，谢谢!

Answer 1

您需要将条件从 WHERE 移动到 ON 子句:

SELECT categories.id, IFNULL(SUM(raw_data.score), 0) as total
FROM categories
LEFT JOIN raw_data ON categories.id = raw_data.category_id
  AND (raw_data.quarter = '2018Q2' OR !raw_data.quarter) 
  AND raw_data.broker_id = 2 
GROUP BY categories.id
ORDER BY total DESC;

SQLFiddle Demo