我正在努力研究如何从 MySQL 查询构建多维数组。并同时删除重复值。以下是查询的输出。 可以看出，索引 3 和 4 是第二个维度的候选者。下面的代码实现了这一点，

但是我在尝试合并第 1 维重复索引 3 和 4 时遇到问题。因此 pets 数组包含两个宠物。

foreach ($Q1RS as $key => $val) {
    $Result[$key]['OwnerID'] = $val['OwnerID'];
    $Result[$key]['Client'] = $val['Owner'];
    $Result[$key]['Since'] = $val['Since'];
    (!is_null($val['Pets? $Result[$key]['Pets'][] = $val['Kitchen']: '';
}

Extract from the resulting array
  3 => 
    array (size=4)
      'OwnerID' => string '4' (length=1)
      'Owner' => string 'Rosie' (length=14)
      'Since' => string '1212-12-12' (length=10)
      'Pets' => 
        array (size=1)
          0 => string 'Poodle' (length=9)
  4 => 
    array (size=4)
      'OwnerID' => string '4' (length=1)
      'Owner' => string 'Rosie' (length=14)
      'Since' => string '1212-12-12' (length=10)
      'Pets' => 
        array (size=1)
          0 => string 'Pony' (length=9)



MySQL result output
array (size=8)
  0 => 
    array (size=4)
      'OwnerID' => string '1' (length=1)
      'Owner' => string 'Bob' (length=7)
      'Since' => string '2012-08-01' (length=10)
      'pets' => null
  1 => 
    array (size=4)
      'OwnerID' => string '2' (length=1)
      'Owner' => string 'Julie' (length=19)
      'Since' => string '2007-07-07' (length=10)
      'pets' => null
  2 => 
    array (size=4)
      'OwnerID' => string '3' (length=1)
      'Owner' => string 'Laing O'Rourke' (length=14)
      'Since' => string '1212-12-12' (length=10)
      'pets' => null
  3 => 
    array (size=4)
      'OwnerID' => string '4' (length=1)
      'Owner' => string 'Rosie' (length=14)
      'Since' => string '1212-12-12' (length=10)
      'pets' => string 'Poodle' (length=9)
  4 => 
    array (size=4)
      'OwnerID' => string '4' (length=1)
      'Owner' => string 'Rosie' (length=14)
      'Since' => string '1212-12-12' (length=10)
      'pets' => string 'Pony' (length=9)
  5 => 
    array (size=4)
      'OwnerID' => string '5' (length=1)
      'Owner' => string 'Gary' (length=10)
      'Since' => string '1212-12-12' (length=10)
      'pets' => null
  6 => 
    array (size=4)
      'OwnerID' => string '6' (length=1)
      'Owner' => string 'Sarah' (length=9)
      'Since' => string '1212-12-12' (length=10)
      'pets' => null
  7 => 
    array (size=4)
      'OwnerID' => string '7' (length=1)
      'Owner' => string 'The Owner' (length=10)
      'Since' => string '2021-07-31' (length=10)
      'pets' => null

表格列如下 所有者 -> ID、姓名、姓氏、地址、手机、电子邮件、自从、 宠物 -> ID、宠物、日期、所有者 ID

$Q1SQL = 'SELECT
        o.ID AS OwnerID,concat(Name,' ',Surname) AS o.Owner,o.Since,p.Pets
     FROM owners AS o
    LEFT JOIN pets AS p
    ON o.ID = p.OwnerID';
    $Statement = $DBConnection->query($Q1SQL);
    $Q1RS = $Statement->fetchAll(PDO::FETCH_ASSOC);
    if (!$Q1RS) {
        die('Query 1 failed!');
    }

重现问题的数据

DROP TABLE IF EXISTS `owners`;
CREATE TABLE `owners` (
  `ID` mediumint unsigned NOT NULL AUTO_INCREMENT,`Name` varchar(50) NOT NULL DEFAULT '',`Surname` varchar(50) NOT NULL DEFAULT '',`Address` varchar(75) NOT NULL DEFAULT '',`Phone` varchar(13) NOT NULL DEFAULT '',`Email` varchar(50) NOT NULL DEFAULT '',`Since` date NOT NULL DEFAULT '1212-12-12',PRIMARY KEY (`ID`),UNIQUE KEY `Email` (`Email`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC;

#
# Data for table "owners"
#

INSERT INTO `owners` VALUES (4,'Rosie','Smith','','0134 123 123','Rosie@gmail.com','2020-12-12'),(8,'Gary','Stevens','Gary@hotmail.com',(10,'Sarah','Sarah@hotmail.com','2020-12-12');

#
# Structure for table "pets"
#

DROP TABLE IF EXISTS `pets`;
CREATE TABLE `pets` (
  `ID` mediumint unsigned NOT NULL AUTO_INCREMENT,`Pet` varchar(30) NOT NULL DEFAULT '',`Date` date NOT NULL DEFAULT '1212-12-12',`OwnerID` mediumint unsigned NOT NULL DEFAULT '0',KEY `OwnerID` (`OwnerID`),CONSTRAINT `pets_ibfk_1` FOREIGN KEY (`OwnerID`) REFERENCES `owners` (`ID`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC;

#
# Data for table "pets"
#

INSERT INTO `pets` VALUES (1,'Shetland Pony','2021-01-01',4),(2,'Jack Russel',10),(3,'Poodle',4);