Php 显示列的sql查询输出

我有这张桌子

id | apple | banana | coconut | pear|
1     1       1       1           0
2     0       0        1          1
3     1       0        0          1

这个sql查询

select tree
from ((select id, 'apple' as tree
       from trees
       where apple = 1
      ) union all
      (select id, 'banana' as tree
       from trees
       where banana = 1
      ) union all
      (select id, 'coconut' as tree
       from trees
       where coconut = 1
      ) union all
      (select id, 'pear' as tree
       from trees
       where pear = 1
      )
     ) t
where id = 1;

输出是

apple 
banana
coconut

我该如何用php编写此代码，以便能够呼应出结果

这就是我目前所拥有的

$sql = " select tree
    from ((select id, 'apple' as tree
           from trees
           where apple = 1
          ) union all
          (select id, 'banana' as tree
           from trees
           where banana = 1
          ) union all
          (select id, 'coconut' as tree
           from trees
           where coconut = 1
          ) union all
          (select id, 'pear' as tree
           from trees
           where pear = 1
          )
         ) t
    where id = '$id'";
 $result = mysqli_query($conn, $sql);

---

但是我不知道在这之后该怎么办我不能进行while循环或只是回显结果它给出了一个错误

您可以简单地使用mysqli\u fetch\u assoc（）循环您的结果：

但是，这样做可能更简单/更有效，它使用列名生成输出数据，在列中的值不是0时回显名称：

$sql = "SELECT * FROM trees WHERE id = '$id'";
$result = mysqli_query($conn, $sql);
while ($row = mysqli_fetch_assoc($result)) {
    foreach ($row as $key => $value) {
        if ($key == 'id') continue;
        if ($value) echo "$key\n";
    }
}

$sql = "SELECT * FROM trees WHERE id = '$id'";
$result = mysqli_query($conn, $sql);
while ($row = mysqli_fetch_assoc($result)) {
    foreach ($row as $key => $value) {
        if ($key == 'id') continue;
        if ($value) echo "$key\n";
    }
}