SQL將兩個選項合併爲一個

我們網站的博客部分是wordpress。我想要做的主要網站的主頁是採取最新的博客文章摘錄，並將其放置在主站點上，並鏈接到博客網站上的文章。我試圖讓SQL語句正常工作，我認爲我有主要部分，但是想把它放到一個SELECT中而不是兩個SELECT中。SQL將兩個選項合併爲一個

我有兩個選擇的原因是爲了確保我得到最新版本的帖子。首先，我嘗試修訂SELECT來查看我是否返回了一行 - 如果我這樣做，我就完成了。如果沒有行（對帖子沒有修訂），請使用第二個SELECT語句。

SELECT TOP 1 * FROM wp_posts 
WHERE post_type = 'revision' 
    AND post_parent IN (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC 

SELECT TOP 1 * FROM wp_posts 
WHERE id IN (SELECT [object_id] 
      FROM wp_term_relationships 
      WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC

我怎麼能這兩個的SELECT合併成一個單一的選擇，所以我可以放心的總是得到一個排回（即最近的博客文章）

在此先感謝。

想到的

來源

2011-07-14 Ed Sinek

的第一件事是使用UNION，然後你可以把結果集的第一行：

SELECT TOP 1 * FROM wp_posts 
WHERE post_type = 'revision' 
    AND post_parent IN (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC 
UNION 
SELECT TOP 1 * FROM wp_posts 
WHERE id IN (SELECT [object_id] 
      FROM wp_term_relationships 
      WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC

UPDATE

以前SQL返回的一個簡單的子查詢第一條記錄：

SELECT TOP 1 * FROM (
SELECT TOP 1 * FROM wp_posts 
WHERE post_type = 'revision' 
    AND post_parent IN (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC 
UNION 
SELECT TOP 1 * FROM wp_posts 
WHERE id IN (SELECT [object_id] 
      FROM wp_term_relationships 
      WHERE term_taxonomy_id = 3) 
ORDER BY post_modified DESC)

來源

2011-07-14 21:00:49

我在想工會爲好，但不與它有太多的經驗，我相信它。有沒有辦法從聯合結果集中選擇前1名？我想不會有什麼大不了的，可以將最多兩行返回給客戶端，而忽略比第一個更多的行。 –

至少你可以重新選擇;讓我更新這個效果;但是，只檢索最多2條記錄_不應對性能產生任何顯着影響。 – 2011-07-14 21:17:23

請問這是否適合您？

SELECT TOP 1 wp_posts.* 
FROM wp_posts, (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3) relations 
WHERE 
    (post_type = 'revision' AND post_parent IN relations) OR 
    (id IN relations) 
ORDER BY post_modified DESC

或者，

SELECT TOP 1 wp_posts.* 
FROM wp_posts, (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3) relations 
WHERE 
    (post_type = 'revision' AND post_parent IN relations AND id NOT IN relations) OR 
    (post_type <> 'revision' AND post_parent NOT IN relations AND id IN relations) 
ORDER BY post_modified DESC

來源

2011-07-14 21:04:31 Dirk

你如何保持正確的排序？ – 2011-07-14 21:05:25

奧普斯，忘了複製一下。謝謝 – Dirk

不過，你如何維持秩序WRT「首先，我試着修改SELECT，看看我是否得到一行返回 - 如果我這樣做，我完成了。如果沒有行（沒有修改的帖子），使用第二個SELECT語句。「？ – 2011-07-14 21:08:17

SELECT TOP 1 * FROM wp_posts 
WHERE (post_type = 'revision' 
    AND post_parent IN (SELECT [object_id] 
       FROM wp_term_relationships 
       WHERE term_taxonomy_id = 3)) 
OR (id IN (SELECT [object_id] 
      FROM wp_term_relationships 
      WHERE term_taxonomy_id = 3)) 
ORDER BY post_modified DESC

來源

2011-07-14 21:05:20

你如何保持正確的排序？ – 2011-07-14 21:06:09

SQL將兩個選項合併爲一個

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