php - MySQL 组按 : How to return multiple rows?

Question

我当前有两个表。我想在一个查询中检索订单的所有相应行。

我当前的代码如下:

$query = '
SELECT * FROM table_a
JOIN table_b ON table_b.order_id = table_a.order_id
WHERE table_a.order_id = '1'
GROUP BY table_a.order_id
';

$result_prepare = $this->DB->prepare($query);
$result_prepare->execute();

$result = $result_prepare->fetchAll(PDO::FETCH_ASSOC);
$query_result = array('result'=>$result);

print_r($query_result);

输出结果仅返回THE FIRST ROW:

Array
(
    [0] => Array
        (
            [order_id] => 1
            [row_id] => 1
            [value] => 100
        )

}

我希望输出结果返回按行分组的所有行。

Array
(
    [0] => Array
        (
            [order_id] => 1
            [rows] => Array
                    (
                        [0] => Array
                            (
                                [row_id] => 1
                                [value] => 100

                            )

                        [1] => Array
                            (
                                [row_id] => 2
                                [value] => 101

                            )

                    )

        )

}

我怎样才能实现这个目标？我需要更改我的 SQL 查询。

Answer 1

您的单行是 MySQL 处理 GROUP BY 的结果，缺少任何聚合函数，例如 COUNT(),SUM(),MIN(),MAX() 。它将组折叠为单行，并且未分组的列的值不确定，因此不值得依赖。

但是，如果您想要一个由 order_id 索引的数组结构，则不需要 GROUP BY。相反，执行一个简单的查询，然后在您的 PHP 代码中，在循环中将其重组为您要查找的格式。

// join in table_a if you need more columns..
// but this query is doable with table_b alone
$query = "
SELECT 
 order_id,
 row_id,
 value
FROM table_b
WHERE order_id = '1'
";

// You do not actually need to prepare/execute this unless you
// are eventually going to pass order_id as a parameter
// You could just use `$this->DB->query($query) for the
// simple query without user input
$result_prepare = $this->DB->prepare($query);
$result_prepare->execute();

$result = $result_prepare->fetchAll(PDO::FETCH_ASSOC);

// $result now is an array with order_id, row_id, value
// Loop over it to build the array you want
$final_output = array();
foreach ($result as $row) {
  $order_id = $row['order_id'];

  // Init sub-array for order_id if not already initialized
  if (!isset($final_output[$order_id])) {
    $final_output[$order_id] = array();
  }
  // Append the row to the sub-array
  $final_output[$order_id][] = array(
    'row_id' => $row['row_id'],
    'value' => $row['value']
  );
  // You could just append [] = $row, but you would still 
  // have the order_id in the sub-array then. You could just 
  // ignore it. That simplifies to:
  // $final_output[$order_id][] = $row;
}

// Format a little different than your output, order_id as array keys
// without a string key called order_id
print_r($final_output);