Question

我的数据库看起来（有点像）：

Table 'posts':
ID  title             text
62  Trees in Europe   You can find fine trees in european woods.
63  Animals in Europe The european fauna is mostly harmless.

Table 'translations':
ID  reference_id  reference_field  translation
36  62            title            Bäume in Europa
37  62            text             Da sind viele Bäume in Europas Wäldern .
44  63            text             Die meisten europäischen Tiere sind harmlos.
47  63            title            Tiere in Europa

reference_field - 表格中的translations提供了翻译文本所代表的posts - 表格字段的信息。

我想有一行SELECT作为结果，给我一个相应的textes的连接，即

ID  title                                  text
62  Trees in Europe // Bäume in Europa     You can find fine trees in european woods. // Du kannst in Europas Wäldern viele Bäume finden.
63  Animals in Europe // Tiere in Europa   The european fauna is mostly harmless. // Die meisten europäischen Tiere sind harmlos.

我尝试了很多，但无法得到它。我遇到的问题是translation列的引用在每一行中都会发生变化。我得到的最接近的是一个列正确连接：

SELECT a.id, 
IF (t.reference_field LIKE "title", CONCAT(left(a.title,20), ' // ', LEFT(t.value, 20)), LEFT(a.title, 20)) AS title, 
IF (t.reference_field LIKE "text", CONCAT(left(a.text,20), ' // ', LEFT(t.value, 20)), LEFT(a.text, 20)) AS summary, 
t.reference_field
FROM posts AS a 
JOIN translations AS t on a.id = t.reference_id 
WHERE a.id=62 
AND t.reference_field IN ('introtext', 'title') 
GROUP BY a.id;

如何修改SQL以便给出预期结果？

任何帮助或提示都表示赞赏！谢谢！

Answer 1

我建议如下：

SELECT p.ID
    ,concat(p.title, ' // ', t_title.translation) AS title
    ,concat(p.text, ' // ', t_text.translation) AS text
FROM posts AS p
LEFT JOIN translations AS t_title ON p.id = t_title.reference_id
    AND t_title.reference_field = 'title'
LEFT JOIN translations AS t_text ON p.id = t_text.reference_id
    AND t_text.reference_field = 'text'

SQL小提琴演示：http://sqlfiddle.com/#!9/5ad47d/4/0

一个小解释：当你多次使用相同的reference_id并且你正在加入这两个表时，你会得到更多的行然后你期望。所以有必要过滤。这就是我使用reference_field并加入2x时间的原因

MySQL条件GROUP_BY

1 个答案: