如何在具有外部联接和分组依据的查询中包括NULL值 [英] How to include NULL values in a query with Outer Join and Group By

问题描述

我有两个带有以下示例数据的表:

I have two tables with the following sample data:

Table 1: `item_name`
| item_id | item_desc |
| 1       | apple     |
| 2       | orange    |
| 3       | banana    |
| 4       | grape     |
| 5       | mango     |

Table 2: `user_items`
| user_id | item_id |
| 127     | 1       |
| 127     | 2       |
| 127     | 4       |
| 128     | 1       |
| 128     | 5       |

我正在尝试使用以下查询选择user_id 127和128拥有的每个item_id的总数，以及对应的item_desc:

I'm trying to select a total of each item_id both user_id 127 and 128 have, along with the corresponding item_desc using the following query:

SELECT IFNULL(COUNT(ui.user_id), 0) AS total, in.item_desc 
FROM user_items AS ui 
RIGHT OUTER JOIN item_name AS in 
    ON ui.item_id = in.item_id 
WHERE ui.user_id IN (127, 128) 
GROUP BY ui.item_id
ORDER BY total DESC

上述查询的结果是:

| total | item_desc |
| 2     | apple     |
| 1     | orange    |
| 1     | grape     |
| 1     | mango     |

但是它不包含item_id 3，banana，我想使用RIGHT OUTER JOIN来检索.我希望得到这样的结果:

but it didn't include item_id 3, banana, which I wanted to retrieve with RIGHT OUTER JOIN. I was hoping to get a result that looked like this:

| total | item_desc |
| 2     | apple     |
| 1     | orange    |
| 1     | grape     |
| 1     | mango     |
| 0     | banana    |

是否有任何方法可以修改查询以得到上述预期结果? 谢谢您的时间.

Is there any way to modify the query to end up with the intended result above? Thank you for your time.

推荐答案

使用count的查询中存在一些错误.这行得通.

There was a little error in your query using count. This works.

select count(ui.item_id) as total, in.item_desc
from   item_name `in`
       left join user_items ui on ui.item_id = in.item_id
                                        and ui.user_id in (127, 128)
group by
       in.item_desc
order by total desc

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