MySQL双左连接，条件OR和组答案

【问题标题】：MySQL double left join, condition OR and groupMySQL双左连接，条件OR和组
【发布时间】：2017-01-25 19:39:50
【问题描述】：

我遇到了一些问题。我尝试计算类别和子类别中的所有文章。

我使用这个查询：

SELECT 
    cat.*, COUNT(art.id) AS total
FROM
    article_categories cat
        LEFT JOIN
    article_categories c2 ON (c2.category_parent = cat.category_id)
        LEFT JOIN
    articles art ON (art.cid = cat.category_id
        OR art.cid = c2.category_id)
WHERE
    cat.category_parent = 0 AND art.st = 1
        AND IF(art.cid IN (2 , 4, 16, 17, 18, 19, 20, 21, 22),
        TO_DAYS(CURDATE()) - TO_DAYS(art.date_edit) < 120,
        art.cid)
GROUP BY IF(c2.category_parent > 0,
    c2.category_parent,
    cat.category_id)
ORDER BY cat.category_order ASC

但对于某些类别，总数 = 36355

当我使用这个查询时：

SELECT 
    *
FROM
    `articles`
WHERE
    st = 1
        AND cid IN (2 , 4, 16, 17, 18, 19, 20, 21, 22)
        AND IF(cid IN (2 , 4, 16, 17, 18, 19, 20, 21, 22),
        TO_DAYS(CURDATE()) - TO_DAYS(date_edit) < 120,
        cid)

总计 = 7730

我做错了什么？

我的桌子：

articles:
- id
- cid
- title
- date_add
- date_edit
- st

article_categories
- category_id
- category_name
- category_order
- category_parent

感谢您的帮助

[编辑]

$sql1 = "SELECT cat.*, COUNT(art.id) AS total FROM article_categories cat LEFT JOIN articles art ON (art.cid = cat.category_id) WHERE cat.category_parent = 0 AND IF(art.cid IN (2 , 4, 16, 17, 18, 19, 20, 21, 22), TO_DAYS(CURDATE()) - TO_DAYS(art.date_edit) < 120, art.cid) GROUP BY art.cid";

$category = array();
foreach ($row as $cat) {
    $total = $cat['total'];
    $sql2 = "SELECT cat.*, COUNT(art.id) AS total FROM article_categories cat LEFT JOIN articles art ON (art.cid = cat.category_id) WHERE cat.category_parent = ".$cat['category_id']." AND IF(art.cid IN (2 , 4, 16, 17, 18, 19, 20, 21, 22), TO_DAYS(CURDATE()) - TO_DAYS(art.date_edit) < 120, art.cid) GROUP BY art.cid";
    foreach ($row2 as $cat2) {
        $total += $cat2['total'];
    }
    $category[] = array('category_id'=> $cat['category_id'], 'total' => $total);
}

【问题讨论】：

您期待什么以及为什么？
我想显示主要类别并与文章一起计数（包含子类别中的所有文章）
你的问题是什么？你期待不同的结果吗？
问题是某些类别的第一次查询计数36355条记录但应该计数7730
您能否解释一下为什么您希望得到这个结果？

标签： mysql group-by left-join

【解决方案1】：

我创建了另一个表：article_categories_rel。

article_categories_rel
- child_id
- parent_id

我自己的新查询：

SELECT
    cat.*,
    COUNT(art.id) as ilosc
FROM
    article_categories cat
LEFT JOIN
    article_categories_rel acr
    ON
        (cat.category_id=acr.parent_id)
LEFT JOIN
    articles art
    ON (
        art.cid = acr.child_id AND
        art.st=1 AND
        if(art.cid in(2,4,16,17,18,19,20,21,22),
        TO_DAYS( curdate( ) ) - TO_DAYS( art.date_edit )<120,
        art.cid)
    )
WHERE
    cat.category_parent=0
GROUP BY
    cat.category_id
ORDER BY
    cat.category_order ASC;

它有效;)

【讨论】：