如何在PHP MySQL JOIN結果上分組？

Question

預期結果：

Berries: blueberry, raspberry, strawberry
Citrus: grapefruit, lime
Pear

---

SQL：

CREATE TABLE IF NOT EXISTS `fruits` (
  `id` varchar(8) NOT NULL,
  `group` varchar(8) NOT NULL,
  `name` varchar(250) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

INSERT INTO `fruits` (`id`, `group`, `name`) VALUES
('03E7', '', 'Berries'),
('0618', '03E7', 'blueberry'),
('051B', '03E7', 'raspberry'),
('02AA', '03E7', 'strawberry'),
('035F', '', 'Citrus'),
('07A5', '035F', 'grapefruit'),
('0633', '035F', 'lime'),
('05E1', '', 'Pear');

當前的PHP：

<?php

header("Content-Type: text/plain");

mysql_connect("localhost", "root", "");
mysql_select_db("test");

$query = mysql_query("SELECT a.name as `group`, b.name as name FROM fruits a LEFT JOIN fruits b ON b.`group` = a.id WHERE a.`group` = ''");

if ($query) {
    while ($row = mysql_fetch_array($query)) {
        echo $row['group'] . ': ' . $row['name'] . "\n";        
    }
    mysql_free_result($query);
}

?>

當前結果：

Berries: blueberry
Berries: raspberry
Berries: strawberry
Citrus: grapefruit
Citrus: lime
Pear: 

Answer 1

SELECT a.name, GROUP_CONCAT(b.name) ... WHERE a.group = '' GROUP BY a.name

總之，您需要一個GROUP BY子句，並且grouped列需要以某種方式聚合（否則，您將只獲得一個值）。 如果這不起作用，您可以使用得到的結果在PHP代碼中輕松完成此操作：

$fruits = array();
while ($row = fetch($query)) {
   //Can be skipped, but you will get notices
   if (!isset($fruits[$row['group']]) {
      $fruits[$row['group']] = array();
   }
   $fruits[$row['group']] = $row['name'];
}

Answer 2

感謝@ExplosionPills發現我有關MySQL GROUP_CONCAT我已更新了返回預期結果的代碼段：

<?php

$query = mysql_query("SELECT a.name as `group`, GROUP_CONCAT(b.name ORDER BY b.name SEPARATOR ', ') as name FROM fruits a LEFT JOIN fruits b ON b.`group` = a.id WHERE a.`group` = '' GROUP BY a.name");

if ($query) {
    while ($row = mysql_fetch_array($query)) {
        $group = $row['group'];
        $name  = $row['name'];

        if (isset($name)) {
            echo $group . ': ' . $name . "\n";
        } else  {
            echo $group . "\n";
        }
    }
    mysql_free_result($query);
}

?>

SQL結果：

顯示第0-2行（共3行，查詢耗時0.0004秒）。

group   | name
--------+--------
Berries | blueberry, raspberry, strawberry
Citrus  | grapefruit, lime
Pear    | NULL

PHP結果：

Berries: blueberry, raspberry, strawberry
Citrus: grapefruit, lime
Pear

歡迎大家進行更好的改進和改進？