我有桌子(大约80’000行),看起来像

id,parentId,col1,col2,col3...
 1,null,'A','B','C'
 2,1,...
 3,...
 4,...
 5,4,...

(一级父母 – 仅限儿童)

我需要获得所有依赖行 –

SELECT ... 
FROM table 
WHERE id = :id OR parentId = :id OR id IN (
    SELECT parentId 
    FROM table 
    WHERE id = :id
    )

但为什么这个请求工作缓慢而不是2请求 – 如果我先在php上获得parentId？

$t = executeQuery('SELECT parentId FROM table WHERE id = :Id;',$id);
if ($t) {
    $id = $t;
}

$t = executeQuery('SELECT * FROM table WHERE id = :id OR parentId = :id ORDER BY id;',$id);

PS：max取决于行数< 70 PPS：

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1   PRIMARY product ALL PRIMARY,parentId    NULL    NULL    NULL    73415   Using where
2   DEPENDENT SUBQUERY  product const   PRIMARY,parentId    PRIMARY 4   const   1

最佳答案
将IN更改为等于=

SELECT ... 
FROM table 
WHERE id = :id OR parentId = :id OR id = (
    SELECT parentId 
    FROM table 
    WHERE id = :id
    )

或将其更改为联接：

SELECT ... 
FROM table 
    inner join ( 
        SELECT parentId 
        FROM table 
        WHERE id = :id
    ) s on s.parentID = table.id or s.parentID = table.parentID