一、需求

已知：库存数据，商品数据。
求：库存剩余数据，出库的商品数据，库存不足/不存在的数据
Tips：根据商品编码扣减库存中的商品数量

二、代码

public function test() {
    list($stockData, $goodsData) = self::getData(); //获取库存数据、商品数据

    $errorMsg = []; //定义出库失败数据
    $stockOutData = []; //定义出库数据

    //已知product_name唯一，处理库存数据以product_name为键
    $stockProductName = array_combine(array_column($stockData, 'product_name'), $stockData);

    self::stockProcess($goodsData, $stockProductName, $stockOutData, $errorMsg);

    //打印结果数据
    echo '<pre>';
    echo '库存剩余数据：<br/>';
    var_export($stockProductName);
    echo '<br/>出库数据：<br/>';
    var_export($stockOutData);
    echo '<br/>出库失败信息：<br/>';
    var_export($errorMsg);
}

/**
 * 返回库存数据、商品数据
 * @return array
 */
public function getData() {
    //库存数据
    $stockData = [
        ['product_name' => 'Goods123', 'number' => 10],
        ['product_name' => 'Goods456', 'number' => 20],
        ['product_name' => 'Goods789', 'number' => 30],
    ];

    //商品数据
    $goodsData = [
        ['goods_name' => '商品1', 'stock_code' => 'Goods123', 'buy_number' => 7],
        ['goods_name' => '商品2', 'stock_code' => 'Goods123', 'buy_number' => 7],
        ['goods_name' => '商品3', 'stock_code' => 'Goods456', 'buy_number' => 7],
        ['goods_name' => '商品4', 'stock_code' => 'Goods456', 'buy_number' => 7],
        ['goods_name' => '商品5', 'stock_code' => 'Goods456', 'buy_number' => 7],
        ['goods_name' => '商品6', 'stock_code' => 'Goods789', 'buy_number' => 30],
        ['goods_name' => '商品7', 'stock_code' => 'Goods321', 'buy_number' => 3],
    ];

    return [$stockData, $goodsData];
}

/**
 * 库存处理方法
 * @param array $goodsData 商品数据
 * @param array $stockProductName 库存编码对应的数据
 * @param array $stockOutData 出库数据
 * @param array $errorMsg 出库失败数据
 */
public function stockProcess($goodsData, &$stockProductName, &$stockOutData, &$errorMsg) {
    //把商品数据循环出库
    foreach ($goodsData as $value) {
        $goodsName = $value['goods_name'];
        $stockCode = $value['stock_code'];
        $buyNumber = $value['buy_number'];

        $msg = "商品 [ {$goodsName} ]，编码 [ {$stockCode} ]：";

        $stockInfo = isset($stockProductName[$stockCode]) ? $stockProductName[$stockCode] : [];
        if (!$stockInfo) {
            $errorMsg[] = "{$msg}库存不存在";
            continue;
        }

        if ($stockInfo['number'] < $buyNumber) {
            $errorMsg[] = "{$msg}库存不足";
            continue;
        }

        //扣减库存数量 = 已有数量 - 商品数量
        $stockProductName[$stockCode]['number'] -= $buyNumber;

        //组装出库数据
        $stockOutData[] = [
            'product_name' => $stockCode,
            'out_number' => $buyNumber
        ];
    }
}

三、打印

库存剩余数据：
array (
  'Goods123' => 
  array (
    'product_name' => 'Goods123',
    'number' => 3,
  ),
  'Goods456' => 
  array (
    'product_name' => 'Goods456',
    'number' => 6,
  ),
  'Goods789' => 
  array (
    'product_name' => 'Goods789',
    'number' => 0,
  ),
)
出库数据：
array (
  0 => 
  array (
    'product_name' => 'Goods123',
    'out_number' => 7,
  ),
  1 => 
  array (
    'product_name' => 'Goods456',
    'out_number' => 7,
  ),
  2 => 
  array (
    'product_name' => 'Goods456',
    'out_number' => 7,
  ),
  3 => 
  array (
    'product_name' => 'Goods789',
    'out_number' => 30,
  ),
)
出库失败信息：
array (
  0 => '商品 [ 商品2 ]，编码 [ Goods123 ]：库存不足',
  1 => '商品 [ 商品5 ]，编码 [ Goods456 ]：库存不足',
  2 => '商品 [ 商品7 ]，编码 [ Goods321 ]：库存不存在',
)