獲取記錄在其他表

Question

不存在我有兩個表：

all_countries

╔════╦═════════════╗ 
║ ID ║ COUNTRY ║ 
╠════╬═════════════╣ 
║ 1 ║ USA   ║ 
║ 2 ║ China  ║ 
║ 3 ║ India  ║ 
║ 4 ║ France  ║ 
║ 5 ║ UK   ║ 
║ 6 ║ Australia ║ 
║ 7 ║ Philippines ║ 
╚════╩═════════════╝ 

supported_countries

╔════════════╦═══════════╦═══════════╗ 
║ COUNTRY_ID ║ COUNTRY ║ FILTER_ID ║ 
╠════════════╬═══════════╬═══════════╣ 
║   1 ║ USA  ║   1 ║ 
║   2 ║ China  ║   1 ║ 
║   3 ║ India  ║   1 ║ 
║   4 ║ France ║   2 ║ 
║   1 ║ USA  ║   2 ║ 
║   6 ║ Australia ║   2 ║ 
╚════════════╩═══════════╩═══════════╝ 

查詢：

SELECT a.* 
FROM all_countries a 
LEFT JOIN supported_countries s 
    ON a.id = s.country_id 
WHERE s.country_id IS NULL; 

所以按照上面的例子我應得。

UK 
Philippines 

它工作正常，但如果，如果我過濾國家的例子，我選擇過濾= 2 我會得到什麼結果爲零。

SELECT a.* 
FROM all_countries a 
LEFT JOIN supported_countries s 
    ON a.id = s.country_id 
WHERE s.filter = 2 AND s.country_id IS NULL; 

應該是我想要得到這樣的結果，如果過濾器= 2

╔════╦═════════════╗ 
║ ID ║ COUNTRY ║ 
╠════╬═════════════╣ 
║ 2 ║ China  ║ 
║ 3 ║ India  ║ 
║ 5 ║ UK   ║ 
║ 7 ║ Philippines ║ 
╚════╩═════════════╝ 

我做了正確的查詢？

Answer 1

添加在ON條款的條件，

SELECT a.* 
FROM all_countries a 
     LEFT JOIN supported_countries s 
      ON a.id = s.country_id AND 
       s.filter_ID = 2  -- <<=== HERE 
WHERE s.country_id IS NULL; 

• SQLFiddle Demo

結果：

╔════╦═════════════╗ 
║ ID ║ COUNTRY ║ 
╠════╬═════════════╣ 
║ 2 ║ China  ║ 
║ 3 ║ India  ║ 
║ 5 ║ UK   ║ 
║ 7 ║ Philippines ║ 
╚════╩═════════════╝