同一張桌子上有多個選擇

Question

我試圖弄清楚它是在同一查詢中進行選擇的一種方法。 我正在處理wordpress數據庫，並且有這些SQL查詢可以自己運行：

SELECT `meta_value` AS 'Name' FROM `wp_postmeta` WHERE `meta_key` =     "myfield1" ORDER BY `post_id` ASC
SELECT `meta_value` AS 'Department' FROM `wp_postmeta` WHERE `meta_key` = "myfield2" ORDER BY `post_id` ASC
SELECT `meta_value` AS 'Location' FROM `wp_postmeta` WHERE `meta_key` = "myfield3" ORDER BY `post_id` ASC
SELECT `meta_value` AS 'Job Title' FROM `wp_postmeta` WHERE `meta_key` = "myfield4" ORDER BY `post_id` ASC
SELECT `meta_value` AS 'Social Number' FROM `wp_postmeta` WHERE `meta_key` = "myfield5" ORDER BY `post_id` ASC

但我想將它們全部放在同一個查詢中，以便稍后可以在報表上導出數據。 這是我嘗試過的：

SELECT  
    (SELECT `meta_value` FROM `wp_postmeta` WHERE `meta_key` = "myfield1" ORDER BY `post_id` ASC) As name,
    (SELECT `meta_value` FROM `wp_postmeta` WHERE `meta_key` = "myfield2" ORDER BY `post_id` ASC) AS department,
    (SELECT `meta_value` FROM `wp_postmeta` WHERE `meta_key` = "myfield3" ORDER BY `post_id` ASC) AS location,
    (SELECT `meta_value` FROM `wp_postmeta` WHERE `meta_key` = "myfield4" ORDER BY `post_id` ASC) AS jobtitle,
    (SELECT `meta_value` FROM `wp_postmeta` WHERE `meta_key` = "myfield5" ORDER BY `post_id` ASC) AS socnumber

但這會使命令不同步。 有人知道如何解決這個問題嗎？

#2014 - Commands out of sync; you can't run this command now 

編輯：我正在查詢wp_postmeta表，它具有4列meta_id，post_id，meta_key和meta_value列。 我從添加的自定義字段（稱為myfield1，保存在meta_key列中）中選擇meta_value。 我按post_id排序，post_id是wordpress中帖子的ID，因此我按時間順序排序。

但是我有5個自定義字段，從myfield1到myfield5。 我想對所有這些查詢一次。

Answer 1

一種方法是使用條件聚合：

SELECT MAX(CASE WHEN `meta_key` = 'myfield1' THEN meta_value END) as Name,
       MAX(CASE WHEN `meta_key` = 'myfield2' THEN meta_value END) as Department,
       MAX(CASE WHEN `meta_key` = 'myfield3' THEN meta_value END) as Location,
       MAX(CASE WHEN `meta_key` = 'myfield4' THEN meta_value END) as JobTitle,
       MAX(CASE WHEN `meta_key` = 'myfield5' THEN meta_value END) as SocialNumber
FROM `wp_postmeta`
WHERE `meta_key` = "myfield5" 
GROPU BY post_id
ORDER B post_id ASC;

Answer 2

您不能選擇別名不同的同一列（“ meta_value” AS“名稱” ...等）並將結果作為一組來獲取。 該列只能有一個名稱！

您可以做的最好的事情是這樣的：

SELECT `meta_value`, `meta_key`
FROM `wp_postmeta`
WHERE `meta_key` IN ("myfield1", "myfield2", "myfield3", "myfield4", "myfield5")
ORDER BY `post_id` ASC

哪一個都將在meta_key列中為您提供所有值在一個結果集中，因此您可以分辨出哪個是哪個。

Answer 3

要獲得具有五列的結果集（每個自定義字段一個），您必須將表自身連接五次...

像這樣：

SELECT
    pm1.meta_value AS 'Name' 
    pm2.meta_value AS 'Department'
    pm3.meta_value AS 'Location'
    pm4.meta_value AS 'Job Title'
    pm5.meta_value AS 'Social Number'

 FROM `wp_postmeta` pm1
    JOIN `wp_postmeta` pm2 ON pm1.post_id = pm2.post_id
    JOIN `wp_postmeta` pm3 ON pm1.post_id = pm3.post_id
    JOIN `wp_postmeta` pm4 ON pm1.post_id = pm4.post_id
    JOIN `wp_postmeta` pm5 ON pm1.post_id = pm5.post_id

WHERE
    pm1.meta_key = "myfield1"
    AND pm2.meta_key = "myfield2"
    AND pm3.meta_key = "myfield3"
    AND pm4.meta_key = "myfield4"
    AND pm5.meta_key = "myfield5"

 ORDER BY `post_id` ASC

我尚未檢查SQL語法，因此，如果出現語法錯誤，請原諒！

假設這是mySQL？