Question

我想在一个sql查询中联接2个表（contact和contact_meta），知道contact_meta有几行

联系

id    fname    lname      email
1     Nick     John       njohn@gmail.com
2     Laura    Pitt       lpitt@gmail.com

Contact_meta

id_contact      contact_meta_key      contact_meta_value
1               Newsletter            yes
1               Level                 weak
2               Newsletter            yes

我尝试过

SELECT * FROM contact as c 
JOIN contact_meta as cm  ON c.id = cm.id_contact

但是如果contact_meta中有多行，我只会得到最后一行。

Array ( 
    [0] => stdClass Object ( [id] => 1 [lname] => Nick [fname] => John [email] => njohn@gmail.com [contact_meta_key] => level [contact_meta_value] => weak ) 
    [1] => stdClass Object ( [id] => 2 [lname] => Laura [fname] => pitt [email] => lpitt@gmail.com [contact_meta_key] => newsletter [contact_meta_value] => yes 
);

此外，我想要[newsletter] => yes instead of [contact_meta_key] => newsletter [contact_meta_value] => yes

我所希望的：

Array ( 
    [0] => stdClass Object ( [id] => 1 [lname] => Nick [fname] => John [email] => njohn@gmail.com [level] => weak [newsletter] => yes) 
    [1] => stdClass Object ( [id] => 2 [lname] => Laura [fname] => pitt [email] => lpitt@gmail.com [newsletter] => yes
);

Answer 1

您需要透视元表。

SELECT c.*,
    MAX(IF(contact_meta_key = 'Newsletter', contact_meta_value, NULL)) AS newsletter,
    MAX(IF(contact_meta_key = 'Level', contact_meta_value, NULL)) AS level
FROM contact AS c
LEFT JOIN contact_meta AS cm ON c.id = cm.id_contact
GROUP BY c.id

DEMO

Answer 2

问题是今天John在contact_meta中有2个条目，但明天可能是5个，而Laura 9个，我在其中存储了许多数据。如果有可能通过1个SQL查询获得用户的所有元数据联系。

我找到了一个解决方案，但我认为不好，因为2条SQL查询（我使用Wordpress）：

$ user = $ wpdb-> get_results（“ SELECT * FROM contact as c JOIN related_browser_contact as rbc ON c.contact_id = rbc.id_contact JOIN浏览器as b ON rbc.id_browser = b.browser_id”）;

            $fellows = array();
            $i=0;
            foreach ($user as $key => $value) {
                $data=array();
                foreach ($user[$i] as $key => $value) {
                    if ( Helper::encrypt_decrypt('decrypt', $value) ){
                        $data[$key] = Helper::encrypt_decrypt('decrypt', $value);
                    }else{
                        $data[$key] = $value;
                    }

                    $metas = $wpdb->get_results( "SELECT contact_meta_key, contact_meta_value FROM contact_meta WHERE id_contact = ".$user[$i]->contact_id );

                    foreach ($metas as $key => $value) {
                        $data[$value->contact_meta_key] = $value->contact_meta_value;
                    }

                }
                $fellows[] = $data;
                $i++;
            }

    print_r($fellows);

在这种情况下，我拥有了所有想要的东西，但是只是想知道SQL查询是否可以做到...

连接具有不同行数的2个表

2 个答案: