Question

到目前为止，我已经得到了这个：

SELECT connections.id,
       connections.word_id,
       connections.order_id,
       connections.top,
       connections.deleted,
       (UNIX_TIMESTAMP() - UNIX_TIMESTAMP(connections.modified)) AS modified_ago,
       words_en.word,
       (CASE WHEN words_en.user_id = 1 THEN "You" ELSE words_en.user_id END) AS created_by
FROM connections, words_en
WHERE connections.word_id = words_en.id AND connections.user_id = 1
ORDER BY connections.order_id

我想添加一些内容，但我无法正确使用语法。

(CASE WHEN words_en.user_id = 1 THEN "You" ELSE words_en.user_id END)这里，当ELSE，而不是ID我想从users表中获取此用户的name_surname列。所以我需要再做一次加入？但既然是在这种情况下，我该怎么办呢？
connections.word_id。除了ID，我还想知道连接表中这个word_id有多少次。但是从列表中排除当前用户。

我希望解释清楚。

Answer 1

SELECT connections.id,
       connections.word_id,
       connections.order_id,
       connections.top,
       connections.deleted,
       (UNIX_TIMESTAMP() - UNIX_TIMESTAMP(connections.modified)) AS modified_ago,
       words_en.word,
       (CASE WHEN words_en.user_id = 1 THEN "You" ELSE users.name_surname END) AS created_by
FROM connections JOIN words
WHERE connections.word_id = words_en.id AND connections.user_id = 1 JOIN users ON users.id=words_en.user_id
ORDER BY connections.order_id

我无法从你的回答中告诉我如何链接用户表，发布表格模式。只是一个疯狂的猜测。

Answer 2

首先，使用ANSI连接重写您的查询，并添加表别名，如下所示：

SELECT c.id,
       c.word_id,
       c.order_id,
       c.top,
       c.deleted,
       (UNIX_TIMESTAMP() - UNIX_TIMESTAMP(c.modified)) AS modified_ago,
       words_en.word,
       (CASE WHEN words_en.user_id = 1 THEN "You" ELSE w.user_id END) AS created_by
FROM connections c
JOIN words_en w ON c.word_id = w.id
WHERE c.user_id = 1
ORDER BY c.order_id

现在扩展此查询变得更加容易：通过w.user_id引入用户，添加另一个加入：

SELECT c.id,
       c.word_id,
       c.order_id,
       c.top,
       c.deleted,
       (UNIX_TIMESTAMP() - UNIX_TIMESTAMP(c.modified)) AS modified_ago,
       words_en.word,
       (CASE WHEN words_en.user_id = 1 THEN "You" ELSE u. name_surname END) AS created_by
FROM connections c
JOIN words_en w ON c.word_id = w.id
JOIN users u ON w.user_id = u.id
WHERE c.user_id = 1
ORDER BY c.order_id

要添加计数，请使用子查询，如下所示：

SELECT c.id,
       c.word_id,
       c.order_id,
       c.top,
       c.deleted,
       (UNIX_TIMESTAMP() - UNIX_TIMESTAMP(c.modified)) AS modified_ago,
       words_en.word,
       (CASE WHEN words_en.user_id = 1 THEN "You" ELSE u. name_surname END) AS created_by,
       (
           SELECT COUNT(*)
           FROM connections cc
           WHERE cc.word_id=c.word_id     -- It's the same word
             AND cc.user_id <> c.user_id  -- user by a different user
       ) as uses_by_others
FROM connections c
JOIN words_en w ON c.word_id = w.id
JOIN users u ON w.user_id = u.id
WHERE c.user_id = 1
ORDER BY c.order_id

具有连接数和案例数的Mysql查询 - 添加更多连接和子查询

2 个答案: