Question

我希望将一个表中的行与另一个表中的行匹配，并且每行应该只匹配一次。我构建了下面的查询，在所有其他方面都可以正常工作，除了我没有进一步调整它以便只能选择一行。

try{$results_pref_school1 = $db->query('SELECT mps.mps_client_ec_no, mcs.mcs_client_ec_no, mps.mps_school_id, mcs.mcs_school_id
                                          FROM match_pref_schools AS mps
                                          INNER JOIN match_current_schools AS mcs
                                          ON mps.mps_school_id = mcs.mcs_school_id
                                          AND mcs.mcs_id IN (SELECT MIN(mcs.mcs_id) 
                                                              FROM match_current_schools AS mcs 
                                                              GROUP BY mcs.mcs_school_id)
                                          ORDER BY mcs.mcs_id');
}catch (Exception $e){
        echo 'Failed to retrieve matched preferred school';
        exit;

}
$matched_school = $results_pref_school1->fetchAll(PDO::FETCH_ASSOC);

$ matched_school的var_dump产生：

Array
(

[1] => Array
    (
        [mps_client_ec_no] => REG5
        [mcs_client_ec_no] => GL98888
        [mps_school_id] => 6
        [mcs_school_id] => 6
    )

[2] => Array
    (
        [mps_client_ec_no] => TAS4752
        [mcs_client_ec_no] => ALF1252
        [mps_school_id] => 14
        [mcs_school_id] => 14
    )

[3] => Array
    (
        [mps_client_ec_no] => MAP002
        [mcs_client_ec_no] => ALF1252
        [mps_school_id] => 14
        [mcs_school_id] => 14
    )

)

在上面的结果中，我希望ALF1252只匹配一次。

Answer 1

@Parts 希望这对您的查询有帮助

在此我添加了索引键，用于删除“使用where;使用连接缓冲区（Block Nested Loop）”，并添加一个匹配的行和您的查询效果现在最好。

QUERY：

SELECT mps.mps_client_ec_no,mps.mps_school_id, mcs.mcs_client_ec_no,  mcs.mcs_school_id 
                                          FROM match_pref_schools AS mps   INNER JOIN match_current_schools AS mcs
                                          ON mps.mps_school_id = mcs.mcs_school_id
                                          where mcs.mcs_id IN (SELECT MIN(mcs.mcs_id) 
                                                              FROM match_current_schools AS mcs 
                                                              GROUP BY mcs.mcs_school_id)
                                          ORDER BY mcs.mcs_id

索引：

KEY `mcs-key` (`mcs_school_id`,`mcs_id`,`mcs_client_ec_no` )

KEY `mps-key` (`mps_school_id`,`mps_client_ec_no`)
INSERT INTO match_current_schools （mcs_id，mcs_client_ec_no，mcs_school_id，mcs_distr_id，mcs_province_id，mcs_client_level_taught，mcs_sub1_id， mcs_sub2_id）VALUES（6，'XYZ'，1,27,3，'HIGH SCHOOL - A LEVEL'，1， 9）;

点击此处：http://sqlfiddle.com/#!9/c4103d/2

我想将一个表中的行与另一个表中的行匹配，并且每行应该只匹配一次

1 个答案: