MYSQL 多表

Question

我想使用多个表来获取最近的帖子(Q)和用户名(句柄)，但是当我尝试使用此代码获取时，它给出了错误

表名称qa_posts和qa_users，并且需要将userid从qa_posts连接到handleqa_users的strong>

SELECT *
FROM qa_posts, qa_users
WHERE type="Q" AND qa_posts.userid = "qa_users.handle"
ORDER BY created DESC
LIMIT 5

错误消息

SELECT *
FROM qa_posts, qa_users
WHERE qa_posts.userid = "qa_users.handle"
ORDER BY created DESC
LIMIT 5

Error 1052: Column 'created' in order clause is ambiguous

实际代码

qa_db_connection();
$query_post = qa_db_query_raw('         
    SELECT *
    FROM qa_posts, qa_users
    WHERE type="Q" AND qa_posts.userid = "qa_users.handle"
    ORDER BY created DESC
    LIMIT 5

') or die(mysql_error());

while($row = mysql_fetch_array($query_post)) {
    echo $row['title'];
    echo '<span style="font-size:65%;font-style:italic">'.$row['created'].'</span>';
    echo '<br/>';
}

请参阅此图片了解表结构

Answer 1

当两个表中都有相同名称的列时，就会出现给定的错误...因此，您必须指定列名称和表名称，如下所示:

table_name.column_name

所以，您的查询应该是这样的:

SELECT *
FROM qa_posts, qa_users
WHERE qa_posts.userid = "qa_users.handle"
ORDER BY qa_posts.created DESC (or put the ORDER BY qa_users.created DESC if you want to make order by `created` of `qa_users` )
LIMIT 5

如果您确实不希望用户 ID 值为“qa_users.handle”，则不应引用它们，并且应具有如下查询:

    SELECT *
    FROM qa_posts, qa_users
    WHERE qa_posts.userid = qa_users.userid AND qa_posts.type="Q" 
    ORDER BY qa_posts.created DESC 
    LIMIT 5

您最好按以下方式使用 JOIN:

    SELECT *
    FROM qa_posts INNER JOIN qa_users ON qa_posts.userid = qa_users.userid 
    WHERE qa_posts.type="Q" 
    ORDER BY qa_posts.created DESC 
    LIMIT 5