php - 如何在mysql select语句上联接4个表？

我在MySQL中有4个表要加入。例

$select = $db->query("SELECT *
                        FROM ads
                       WHERE ad_pic='1'
                         AND ad_status = '1'
                    ORDER BY ad_id DESC LIMIT 0,4");

while ($fetch = $db->fetch($select)) {

    $iquery = $db->query("SELECT *
                            FROM images
                           WHERE img_ads_id = '" . intval($fetch['ad_id']) . "'
                             AND img_status = '1'
                           LIMIT 1");
    $thumb = $db->fetch($iquery);

    $uselect = $db->query("SELECT *
                             FROM users
                            WHERE user_id = '".intval($fetch['ad_userid'])."'
                              AND user_status = '1'
                            LIMIT 1");
    $ufetch = $db->fetch($uselect);

    $cselect = $db->query("SELECT *
                             FROM category
                            WHERE cat_slug = '".safe_func($fetch['ad_category'])."'
                            LIMIT 1");
    $cfetch = $db->fetch($cselect);

}

我想知道在一个select语句中加入这些的方式。

ads table

ad_id   ad_userid   ad_category
-------------------------------
1       2           5

images table

img_id  img_ads_id
-------------------------------
1       1

users table

user_id     user_name
-------------------------------
2           John

category table

cat_id   cat_name
-------------------------------
5        Vehicles

最佳答案

SELECT *
FROM ads AS a
LEFT JOIN images AS i ON i.img_ads_id = a.ad_id AND i.img_status = 1
LEFT JOIN users AS u ON u.id = a.ad_userid AND u.user_status = 1
LEFT JOIN category AS c ON c.cat_slug = a.ad_category
WHERE a.ad_pic = 1
AND a.ad_status = 1
ORDER BY a.ad_id DESC
LIMIT 0,4

如果广告必须包含图片，用户或类别，则可以使用JOIN代替LEFT JOIN。如果一则广告可以包含多个图片，用户或类别，则您将需要更复杂的查询。

关于php - 如何在mysql select语句上联接4个表？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/5227313/