查询数据库后打印出部分唯一的数据 [英] Printing out partially unique data after querying a db

问题描述

我在弄清楚如何像我需要的那样使用表格数据时遇到了麻烦……我的表格包含一个类别名称列(对于许多子类别具有相同的值)，另一列包含子类别名称.

I am having trouble finguring out how to use the table data like I need to... my table consists of a category name column (which has the same value for many subcategories) and the other column contains subcategory names.

例如:

col1        col2
------------------
apples      fruits
oranges     fruits
pears       fruits
honda       cars
volvo       cars
audi        cars

我正在尝试编写一个 select 语句，该语句从数据库中选择所有数据并仅打印一次类别名称，同时打印出该特定类别名称包含的所有子类别.

I am trying to write a select statement that selects all the data from the database and prints out the category name once ONLY, while printing out all subcategories that, that particular category name includes.

类似于:

水果:

• 苹果
• 橙子
• 梨

汽车:

• 本田
• 沃尔沃
• 奥迪

推荐答案

SELECT
    col2,
    GROUP_CONCAT(col1 SEPARATOR ',') as stuff
FROM table1
GROUP BY col2

如果你想在名字前面加上'-'，你可以使用CONCAT('-',col1) 而不是col1.

If you want the '-' in front of the names you can use CONCAT('-',col1) instead of col1.

这段php代码会将结果转换成一维数组

This php code will transform the result into a 1 dimensional array

$conn = new mysqli('host','user','pass','db_name');

if ($conn->connect_errno) {
    printf("Connect failed: %s\n", $conn->connect_error);
    exit();
}

if (!($rs = $conn->query("
        SELECT
            col2,
            GROUP_CONCAT(col1 SEPARATOR ',') as stuff
        FROM table1
        GROUP BY col2
    "))) {
    printf("Error: %s\n", $conn->error);
    exit();
}


$result = array();
while ($row = $rs->fetch_object()){
    $result[] = $row->col2;
    if(!empty($row->stuff)) $result = array_merge($result,explode(',',$row->stuff));
}

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