Question

好的，这里有。我想创建一个显示这个的视图：

+---------+---------+-------+--------+------------+---------------------+---------------+-------------------+-------------+
| post_id | status  | title | body   | ip_address | time_stamp          | category_name | sub_category_name | post_type   |
+---------+---------+-------+--------+------------+---------------------+---------------+-------------------+-------------+
|       1 | enabled | test  | test 2 |            | 2010-05-20 01:22:17 | For Sale      | Computers         | transaction |
+---------+---------+-------+--------+------------+---------------------+---------------+-------------------+-------------+
1 row in set (0.00 sec)

执行此操作的查询是：

SELECT post.id AS post_id, 
post.status AS status, 
post_data.title AS title, 
post_data.body AS body, 
post_data.ip_address AS ip_address, 
post_data.time_stamp AS time_stamp, 
post_category.name AS category_name, 
post_sub_category.name AS sub_category_name, 
post_category.type AS post_type 
FROM post,
(
SELECT * FROM post_data WHERE post_data.post_id = post_id ORDER BY post_data.post_id DESC LIMIT 1
) AS post_data,
post_sub_category, 
post_category 
WHERE 
post.sub_category_id = post_sub_category.id AND 
post_sub_category.category_id = post_category.id

但是，由于它有嵌套查询，我不能将它用作视图。目前，我能想到的最好的查询是一个视图：

SELECT
post.id AS post_id, 
post.status AS status, 
post_data.title AS title, 
post_data.body AS body, 
post_data.ip_address AS ip_address, 
post_data.time_stamp AS time_stamp, 
post_category.name AS category_name, 
post_sub_category.name AS sub_category_name, 
post_category.type AS post_type 
FROM post,
post_data,
post_sub_category, 
post_category 
WHERE 
post.sub_category_id = post_sub_category.id AND 
post_sub_category.category_id = post_category.id
ORDER BY post_data.id DESC

但那只是回归：

+---------+---------+-------+-----------+----------------+---------------------+---------------+-------------------+-------------+
| post_id | status  | title | body      | ip_address     | time_stamp          | category_name | sub_category_name | post_type   |
+---------+---------+-------+-----------+----------------+---------------------+---------------+-------------------+-------------+
|       1 | enabled | test  | test 2    |                | 2010-05-20 01:22:17 | For Sale      | Computers         | transaction |
|       1 | enabled | TEST  | TEST BODY | 192.168.10.155 | 2010-05-19 23:09:15 | For Sale      | Computers         | transaction |
+---------+---------+-------+-----------+----------------+---------------------+---------------+-------------------+-------------+
2 rows in set (0.00 sec)

我每个post_id只需要一行，我希望它是最新的一行。有没有人有什么建议？在处理软删除和诸如此类的事情时，我正在使用视图来尝试让生活变得更轻松，理论上，从长远来看，我还可以更轻松地查询我想要的数据。

提前非常感谢！

Answer 1

您可以使用

 GROUP BY post_data.post_id HAVING MAX(post_data.time_stamp)

只获得最新的一行。所以完整的查询可能如下所示：

SELECT
post.id AS post_id, 
post.status AS status, 
post_data.title AS title, 
post_data.body AS body, 
post_data.ip_address AS ip_address, 
post_data.time_stamp AS time_stamp, 
post_category.name AS category_name, 
post_sub_category.name AS sub_category_name, 
post_category.type AS post_type 
FROM post,
post_data,
post_sub_category, 
post_category 
WHERE 
post.sub_category_id = post_sub_category.id AND 
post_sub_category.category_id = post_category.id
GROUP BY post_data.post_id HAVING MAX(post_data.time_stamp)
ORDER BY post_data.id DESC

Answer 2

这样的东西会有用吗？我不确定它，因为它包含一个子查询，它给你带来麻烦，但是在另一个地方......

SELECT post.id AS post_id, 
   post.status AS status, 
   post_data.title AS title, 
   post_data.body AS body, 
   post_data.ip_address AS ip_address, 
   post_data.time_stamp AS time_stamp, 
   post_category.name AS category_name, 
   post_sub_category.name AS sub_category_name, 
   post_category.type AS post_type 
FROM post,
     post_data,
     post_sub_category, 
     post_category 
WHERE post.sub_category_id          = post_sub_category.id AND 
      post_sub_category.category_id = post_category.id     AND
      post_data.post_id             = post_id              AND
      post_data.time_stamp = (SELECT MAX(time_stamp)
                                  FROM post_data
                                  WHERE post_data.post_id = post_id);

表演可能也不值得回家。

MySQL - 在视图中获取不同的行

2 个答案: