爲每個用戶連接MySQL查詢爲單行

Question

我有一個查詢，我試圖讓另一個表內的每個用戶的值到結果中的一個輸出行。

SELECT DISTINCT table1.ID, table1.username, table1.display_name, 
       CASE WHEN table2.meta_key = 'vgm' THEN table2.meta_value END VGM, 
       CASE WHEN table2.meta_key = 'year_completed' THEN table2.meta_value END 'Year Completed', 
       CASE WHEN table2.meta_key = 'status' THEN table2.meta_value END Status, 
       CASE WHEN table2.meta_key = 'military_grade' THEN table2.meta_value END 'Military Grade' 
      FROM table1, table2 
      WHERE table1.ID = table2.user_id 

我最終得到的結果如下。如果可能的話，我希望所有的用戶信息都在一行中。任何人有任何建議？謝謝。

<table> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
</tr> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>Baja</td> 
 
<td>NULL</td> 
 
</tr> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
<td>NULL</td> 
 
<td>112</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
</tr> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>Subt</td> 
 
</tr> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
<td>No</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
<td>NULL</td> 
 
</tr> 
 
</table>

表1是作爲這種：

<table> 
 
<tr> 
 
<td>ID</td> 
 
<td>NAME</td> 
 
<td>EMAIL</td> 
 
</tr> 
 
<tr> 
 
<td>3</td> 
 
<td>user1</td> 
 
<td>Username Last</td> 
 
</tr> 
 
<tr> 
 
<td>4</td> 
 
<td>user2</td> 
 
<td>Username2 Last2</td> 
 
</tr> 
 
</table>

表2是這樣：

<table> 
 
<tr> 
 
<td>ID</td> 
 
<td>USER_ID</td> 
 
<td>META_KEY</td> 
 
<td>META_VALUE</td> 
 
</tr> 
 
<tr> 
 
<td>1</td> 
 
<td>3</td> 
 
<td>Key 1</td> 
 
<td>Value 1</td> 
 
</tr> 
 
<tr> 
 
<td>1</td> 
 
<td>3</td> 
 
<td>Key 2</td> 
 
<td>Value 2</td> 
 
</tr> 
 
<tr> 
 
<td>1</td> 
 
<td>4</td> 
 
<td>Key 1</td> 
 
<td>Value 1</td> 
 
</tr> 
 
<tr> 
 
<td>1</td> 
 
<td>4</td> 
 
<td>Key 2</td> 
 
<td>Value 2</td> 
 
</tr> 
 
</table>

Answer 1

下面的查詢之間的主要區別和你的是我拿table2併爲每個meta_key子查詢，然後使用LEFT JOIN加入這些子查詢table1。這應該會爲每個用戶創建一條記錄。

你的表結構和查詢有一些不一致的地方，比如，table1有user_name和display_name但是模式有NAME和EMAIL。我繼續使用您的查詢的字段名稱。

SQL查詢

SELECT 
    users.ID AS Id, 
    users.username AS UserName, 
    users.display_name AS DisplayName, 
    vgm.meta_value AS VGM, 
    year_completed.meta_value AS YearCompleted, 
    status.meta_value AS Status, 
    military_grade.meta_value AS MilitaryGrade 

-- Users -- 
FROM table1 AS users 

-- VGM -- 
LEFT JOIN (
    SELECT user_id, meta_key, meta_value 
    FROM table2 
    WHERE meta_key = 'vgm') 
AS vgm ON users.ID = vgm.user_id 

-- Year Completed -- 
LEFT JOIN (
    SELECT user_id, meta_key, meta_value 
    FROM table2 
    WHERE meta_key = 'year_completed') 
AS year_completed ON users.ID = year_completed.user_id 

-- Status -- 
LEFT JOIN (
    SELECT user_id, meta_key, meta_value 
    FROM table2 
    WHERE meta_key = 'status') 
AS status ON users.ID = status.user_id 

-- Military Grade -- 
LEFT JOIN (
    SELECT user_id, meta_key, meta_value 
    FROM table2 
    WHERE meta_key = 'military_grade') 
AS military_grade ON users.ID = status.user_id