php通过日期问题加入2个表

如何解决php通过日期问题加入2个表

| 所以我有2个没有任何共同点的表，我想按它们的日期列来存储它们 所以table1像这样： 表格1 ID post_id 发布日期 表2 ID comment_id comment_date 我要显示的是table1，table2中的所有内容，并按日期排序 我尝试过类似的东西

SELECT * FROM table1 INNER JOIN table2 ORDER BY post_date DESC,comment_date DESC

问题是我不知道如何识别在while（rows = MysqL_fetch_assoc（））内部使用的项目（发布或评论），因为我具有不同的列名。 解决方案是：

                SELECT * FROM (
                SELECT 1 AS `table`,`col1` AS `userid`,`col2` AS `cat`,`col3` AS `item_id`,`title` AS `title`,etc...,`date` AS `date` FROM `table1`
                UNION
                SELECT 2 AS `table`,NULL AS `title`,`date` AS `date` FROM `table2`
            ) AS tb
            ORDER BY `date` DESC

    

解决方法

        尝试

UNION

，并使用新的常量列指示正在输出的表，并使用

AS

使列名相同。 周围的

SELECT

可能使您可以一起订购。

SELECT * FROM (
    (SELECT 1 AS `table`,`id`,`post_id` AS `table_id`,`post_date` AS `date` FROM `table1`)
    UNION
    (SELECT 2 AS `table`,`comment_id` AS `table_id`,`comment_date` AS `date` FROM `table2`)
)
ORDER BY `date` DESC

那将需要测试，不确定是否允许。     ,        若要将帖子链接到评论，则必须重新设计数据库。 给定这些表

table1

    id
    post_id
    post_date

table2

    id
    comment_id
    comment_date

注释应该是属于帖子的注释，因此您需要更改表，以便其结构变为：

table post

    id         /*id of a post*/
    user_id    /*which user posted this*/
    post_date  /*when?*/
    post_text  /*the text inside the post*/

table comments

    id            /*id of a comment*/
    post_id       /*which post does this comment belong to*/
    user_id       /*who posted this*/
    comment_date  /*when*/
    comment_text  /*text of the comment*/

现在，您可以通过执行以下操作加入此操作：

$post_id = mysql_real_escape_string($_GET[\'post_id\']);

/*select all comments belonging to a post*/
$query = \"SELECT c.user_id,c.comment_date,c.comment_text FROM posts p
          INNER JOIN comments c ON (c.post_id = p.id)
          WHERE p.id = \'$post_id\'\";
....

在当前设计中，由于两者之间没有关系，因此无法可靠地连接它们。     ,        

                SELECT * FROM (
            SELECT 1 AS `table`,`col1` AS `userid`,`col2` AS `cat`,`col3` AS `item_id`,`title` AS `title`,etc...,`date` AS `date` FROM `table1`
            UNION
            SELECT 2 AS `table`,NULL AS `title`,`date` AS `date` FROM `table2`
        ) AS tb
        ORDER BY `date` DESC