Question

我正在尝试搜索具有给定标记的问题。

如何解决以下问题？

表格

questions          |     tags
-------------------|-----------------
  question_id      |     tag
  title            |     question_id
  was_sent_at_time |

我的代码

    SELECT question_id, title
    FROM questions
    WHERE question_id IN
    ( 
        SELECT question_id
        FROM questions
        ORDER BY was_sent_at_time      // problem here
        DESC LIMIT 50
    ) 
    AND tag IN                         // problem here
    (
        SELECT tag FROM tags
        WHERE tag = $1
        AND WHERE question_id IN (                                                                               
            SELECT question_id
            FROM questions
            ORDER BY was_sent_at_time
            DESC LIMIT 50
        )
    )
    ORDER BY was_sent_at_time
    DESC LIMIT 50;

我跑步并获得

Warning: pg_prepare() [function.pg-prepare]: Query failed: ERROR: syntax error at or near "WHERE" LINE 14: AND WHERE question_id IN ( ^ in /var/www/codes/handlers/searches/handle_questions_by_tag.php on line 30

我显然应该使用JOIN。但是，我不想将标签作为输出到我的最终结果。

Answer 1

尝试：

SELECT q.question_id, q.title
    FROM questions      q
        INNER JOIN tags t ON q.question_id=t.question_id
    WHERE tag = $1 
    ORDER BY q.was_sent_at_time
    DESC LIMIT 50

Answer 2

听起来你只是想要这个：

SELECT questions.question_id, questions.title
FROM questions
WHERE EXISTS 
  (SELECT 1 
   FROM tags 
   WHERE tag = $1 AND tags.question_id = questions.question_id
  )
ORDER BY was_sent_at_time DESC
LIMIT 50;

你也可以像JOIN这样使用：

SELECT questions.question_id, questions.title
FROM questions
INNER JOIN tags ON (tags.question_id = questions.question_id)
GROUP BY questions.question_id
ORDER BY was_sent_at_time DESC
LIMIT 50;

使用JOIN本身并不能确定您获得的行或列。您可以通过添加适当的SQL子句来确定它。

Answer 3

JOINS并不意味着您将在最终结果中获得标签。如果您不想看标签，可以保持指定的列相同。

Answer 4

select questions.* from questions, tags
where questions.questionid = tags.questionid
and tags.tag = $1

但是，我建议在问题和标签之间存在多对多关系（一个问题可以包含许多标签，一个标签可以与许多问题相关联）。

Answer 5

SELECT questions.question_id, questions.title 
FROM questions 
INNER JOIN tags ON questions.question_id=tags.question_id 
WHERE tags.tag=$1 
ORDER BY questions.was_sent_at_time 
DESC LIMIT 50;

我认为会这样做......

Answer 6

怎么样：

SELECT questions.question_id, questions.title, questions.was_sent_at_time
FROM questions
JOIN tags ON questions.question_id = tags.question_id
WHERE tags.tag = 'whatever'
ORDER BY questions.was_sent_at_time

这应该不需要输出中的tags表中的任何内容，尽管我实际上没有测试过它。

在SQL中使用其他表作为WHERE条件

6 个答案: