Question

我想要任何类型的JOIN。我正在使用PHP构建两个表的RSS提要，我想从两个表中选择所有行，保持行分开但按常用created列排序。

例如，如果我有一个表foo：

id      downloads   views   created
-----------------------------------------------
1       12          23      2011-07-22 00:10:16
2       51          900     2011-07-22 10:11:45
3       8           80      2011-07-23 04:12:18

表格bar：

id      title       body    created
-----------------------------------------------
1       foo         ogblog  2011-07-21 10:54:07
3       bar         zip     2011-07-24 10:54:07
4       zip         bar     2011-07-25 10:54:07

我想从通用created列排序的两个表中选择所有数据，因此示例结果集将是（忽略bar.id，因为它不需要）：< / p>

id      title       body        downloads   views   created             | table
-------------------------------------------------------------------------------
NULL    bar         zip         NULL        NULL    2011-07-24 10:54:07 | bar
NULL    foo         ogblog      NULL        NULL    2011-07-21 10:54:07 | bar
1       NULL        NULL        12          23      2011-07-22 00:10:16 | foo
2       NULL        NULL        51          900     2011-07-22 10:11:45 | foo
3       NULL        NULL        8           80      2011-07-23 04:12:18 | foo
NULL    zip         bar         NULL        NULL    2011-07-25 10:54:07 | bar

不需要table列;我添加它是为了让事情更容易理解。

希望很明显我想做什么;而不是从两个表中的列生成行JOIN，我希望获得具有公共列布局的所有行数据，其中表中不存在的任何列都具有NULL投入其中。

如果您需要澄清，请告诉我。

Answer 1

使用虚拟列来计算不同的结构，使用联合来加入它们，使用父选择来处理排序：

SELECT * FROM (
    (SELECT foo.id, NULL AS title, NULL AS body, foo.downloads, foo.views, foo.created FROM foo)
    UNION ALL
    (SELECT NULL AS id, bar.title, bar.body, NULL AS downloads, NULL AS views, bar.created FROM bar)
) results
ORDER BY created ASC

Answer 2

扩展@Brendan Bullen的建议，这是一个使用UNION ALL的示例，它应该适合您：

SELECT id as id, NULL as title, NULL as body, downloads as downloads, 
  views as views, created as created, 'foo' as table_name
FROM foo
UNION ALL
SELECT NULL as id, title as title, body as body, NULL as downloads, 
  NULL as views, created as created, 'bar' as table_name
FROM bar
ORDER BY created ASC

从两个表中选择单独的行，按日期排序

2 个答案: