MySQL查詢加入GROUP_CONCAT

Question

我有以下查詢，

SELECT 
    p.id AS parent, GROUP_CONCAT(c.id) AS children 
FROM 
    rev_r_clients AS p 
JOIN 
    rev_r_clients AS c ON c.parent_client_id = p.id 
GROUP BY 
    p.id 

它得到id爲家長和家長的孩子。從那以後，我送的映射id使用以下功能陣列，

$parents = Array(); 

while ($row = $res->fetch_assoc()) { 
    $parents[$row['parent']] = explode(',',$row['children']); 
} 

我需要它從另一個表獲得username（rev_users）爲好，怎麼能這樣做？

Answer 1

如果你不想與兩個查詢（或者使用子查詢或者一個MySQL的交易），以實現這一目標，那麼你可以Concat的是這樣的：

SELECT 
    p.id AS parent_id, p_u.name, GROUP_CONCAT(CONCAT(c.id, '-', c_u.name)) AS children 
FROM 
    rev_r_clients AS p 
JOIN 
    rev_r_clients AS c ON c.parent_client_id = p.id 
JOIN 
    rev_users c_u ON c_u.id= c.id 
JOIN 
    rev_users p_u ON p.id = p_u.id 
GROUP BY 
    p.id 

不過要小心這樣做。 GROUP_CONCAT可以獲得多大的限制。查看文檔http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

而且你的代碼看起來像

$parents = Array(); 
while($row = $res->fetch_assoc()) { 
    $children = explode(',',$row['children']); 
    foreach($children as $child){ 
    $child_info = explode('-', $child); 
    if(!isset($parents[$row['parent_id']])){ 
     $parents[$row['parent']] = array(
     'id' => $row['parent'], 
     'name' => $row['name'], 
     'children' => array() 
    ) 
    } 
    $parents[$row['parent']]['children'][] = array(
     'id' => $child_info[0], 
     'name' => $child_info[1] 
    ); 
    } 
} 

最後要小心使用你的CONCAT功能的分離，你知道會不會是在名稱中。