mysql：使用meeting_id = x記錄所有記錄，並且它的父項可用，但不關心它是否可用？

Question

如何選擇符合以下條件的所有記錄：

以meeting_id = x記錄所有記錄，並且它的父項可用或者沒有父項，但不在意是否可用本身？

table people: 
id, name, address, meeting_id, available, parent_id 

Answer 1

select * from people outt 
    where meeting_id = x and 
    (parent_id is null or exists (select 1 from people inn where inn.id = outt.parent_id and available = 1)) 

Answer 2

未經測試，請嘗試。如果沒有父COALESCE將選擇第二PARAM和使用自動1.

SELECT * FROM people 
    WHERE 
    meeting_id=x AND 
    (COALESCE((SELECT available FROM people AS parent WHERE id=parent_id), 1)) 

Answer 3

您可以用做JOIN：

SELECT 
    child.*, 
    parent.name 
FROM 
    people child 
LEFT JOIN 
    people parent on (child.parent_id = parent.id) 
WHERE 
    (parent.available = 1 or parent.id IS NULL) AND 
    child.meeting_id = x; 

見http://dev.mysql.com/doc/refman/5.0/en/join.html的細節