MYSQL作为查询使用子查询而不是2个查询(php)

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,        1, ...
 4,     null, ...
 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

转载注明原文:MYSQL作为查询使用子查询而不是2个查询(php) - 代码日志