mySql - 從表中獲取相關值

Question

好吧，我會盡可能地保持清醒，但請忍受我 - 這是一個漫長的一周:)

我們有一個表格，結構如下：

+----+----------+---------+------------------+
| id | field_id | user_id |      value       |
+----+----------+---------+------------------+
|  1 | Country  |       2 | USA              |
|  2 | Country  |       3 | USA              |
|  3 | Country  |       4 | CA               |
|  4 | Country  |       5 | MX               |
|  5 | Province |       2 | FL               |
|  6 | Province |       3 | GA               |
|  7 | Province |       4 | British Columbia |
|  8 | Province |       5 | Sonara           |
|  9 | City     |       2 | Orlando          |
| 10 | City     |       3 | Brunswick        |
| 11 | City     |       4 | Vancouver        |
| 12 | City     |       5 | Nogalas          |
+----+----------+---------+------------------+`

我們需要（希望）一個查詢返回所有Country - State / Province - City組合，以便動態生成JSON文件。

有效的東西

"SELECT all Provinces and Cities WHERE Country = 'USA'"

（但當然，我們的db表的結構 - 遺憾的是無法更改 - 它的復雜程度要高得多。

共享共同“user_id”的任何值可以安全地假設為“一起”（即，user_id 2具有“USA”表示“Country”，“FL”表示“省”，“Orlando”表示“City” ）。

最終結果我們試圖創建一個類似於下面的json文件。

{
"USA": {
    "Florida": [
        {"City": "Orlando"},
        {"City": "Palm Beach"}
    ],
    "Georgia": [
        {"City": "Atlanta"},
        {"City": "Brunswick"}
    ]
}, 
"Canada": {
    "Alberta": [
        {"City": "Calgary"}
    ],
    "Ontario": [
        {"City": "Atlanta"},
        {"City": "Brunswick"}
    ]
}
}

Answer 1

有了這個查詢和一些循環的結果，你應該能夠根據需要生成你的Json

SQL小提琴

MySQL 5.6架構設置 ：

CREATE TABLE t
    (`id` int, `field_id` varchar(8), `user_id` int, `value` varchar(16))
;

INSERT INTO t
    (`id`, `field_id`, `user_id`, `value`)
VALUES
    (1, 'Country', 2, 'USA'),
    (2, 'Country', 3, 'USA'),
    (3, 'Country', 4, 'CA'),
    (4, 'Country', 5, 'MX'),
    (5, 'Province', 2, 'FL'),
    (6, 'Province', 3, 'GA'),
    (7, 'Province', 4, 'British Columbia'),
    (8, 'Province', 5, 'Sonara'),
    (9, 'City', 2, 'Orlando'),
    (10, 'City', 3, 'Brunswick'),
    (11, 'City', 4, 'Vancouver'),
    (12, 'City', 5, 'Nogalas')
;

查詢1 ：

SELECT 
    tc.`value` as Country,  
    tp.`value` as Province,  
    tcy.`value` as City
FROM (
        SELECT `value`, user_id FROM t WHERE field_id = "Country"
    ) as tc
    LEFT JOIN (
            SELECT `value`, user_id FROM t WHERE field_id = "Province"
        ) as tp
        ON tc.user_id = tp.user_id
    LEFT JOIN (
            SELECT `value`, user_id FROM t WHERE field_id = "City"
        ) as tcy
        ON tp.user_id = tcy.user_id

結果 ：

|Country|         Province |      City |
|-------|------------------|-----------|
|   USA |               FL |   Orlando |
|   USA |               GA | Brunswick |
|    CA | British Columbia | Vancouver |
|    MX |           Sonara |   Nogalas |