mysql查询：获取多表选择相关表的最后一行

Question

我有 2 个这样的表格

products

• 身份证
• 标题

plans

• 身份证
• product_id
• 价格
• 类型

基本上这个想法是为每个产品设置多个价格，每个产品的最后一个计划将是它的当前价格，如果它被删除或过期，它将回退到之前的计划

因此，如果一个产品有 2 个 ID 为 (1, 2) 的计划，那么带有 id = 2 的计划将是其当前价格

我想展示他们最后计划的产品type = off

这是由 Laravel ORM Eloquent 生成的 SQL Query

select * from `products` where exists
        (select * from `plans` where `products`.`id` = `plans`.`product_id`
                and `type` = 'off' 
                and `plans`.`deleted_at` is null) 
        and `products`.`deleted_at` is null

问题是它不会检查它会在所有计划中搜索的最后/当前计划...所以即使id = 2 类型的计划没有关闭并且如果plan.id = 1 类型关闭我仍然会将在查询中包含此产品
这是php代码：

$wonder_product = Product::whereHas('CurrentPlan', function ($q) {
    $q->where('type', 'off');
})->get();

Answer 1

尝试使用 GROUP BY 子查询：

$wonder_product = Product::whereHas('CurrentPlan', function ($q) {
    $q->where('type', 'off')
    ->whereIn('id', function ($subquery) {
        $subquery
        ->from(with(new CurrentPlan)->getTable())
        ->select(DB:raw('MAX(id)'))
        ->groupBy('product_id');
    });
})->get();

或者，如果您可以使用原始子查询：

$wonder_product = Product::whereHas('CurrentPlan', function ($q) {
    $q->where('type', 'off')
      ->whereRaw('id in (select max(id) from plans group by product_id)')
})->get();

如果我没记错的话，这两种方法都应该生成这样的查询：

select * from `products`
where exists (
        select * from `plans`
        where `products`.`id` = `plans`.`product_id`
          and `type` = 'off' 
          and `plans`.`deleted_at` is null
          and id in (select max(id) from plans group by product_id)
  ) 
  and `products`.`deleted_at` is null

但如果是我，我可能会写一个这样的原始查询：

$wonder_product = Product::hydrateRaw('
    select products.*
    from products
    where 'off' = (
      select plans.type
      from plans
      where plans.product_id = products.id
        and plans.deleted_at is null
      order by plans.id desc
      limit 1
    )
    and products.deleted_at is null
');

Answer 2

你应该改用whereDoesntHave

return Product::whereDoesntHave('plans', function ($q) {
    $q->where('type', 'off');
})->with('plans')->get();

工作示例：

products migration

Schema::create('products', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->string('title');
    $table->timestamps();
});

plans migration

Schema::create('plans', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->unsignedBigInteger('product_id');
    $table->foreign('product_id')->references('id')->on('products')
                                 ->onDelete('cascade');
    $table->decimal('price');
    $table->string('type');
    $table->timestamps();
});

Product Model Relationship

public function plans()
{
    return $this->hasMany(Plan::class);
}

Plan Model Relationship

public function product()
{
    return $this->belongsTo(Product::class);
}

Sample Data Seeder

$productWithOnePlanOff = Product::create([
    'title' => 'A product with one of its plans off'
]);
$productWithOnePlanOff->plans()->createMany([
    ['price' => rand(1, 50), 'type' => 'off'],
    ['price' => rand(50, 100), 'type' => 'on']
]);
$productWithNoPlanOff = Product::create([
    'title' => 'A product with none of its plans off'
]);
$productWithNoPlanOff->plans()->createMany([
    ['price' => rand(1, 50), 'type' => 'on'],
    ['price' => rand(50, 100), 'type' => 'on']
]);

查询部分和结果

WhereHas 查找其 ANY 的相关模型与查询条件匹配的模型

return Product::whereHas('plans', function ($q) {
    $q->where('type', 'off');
})->with('plans')->get();

结果

[
    {
        "id": 1,
        "title": "A product with one of its plans off",
        "created_at": "2019-09-03 16:30:30",
        "updated_at": "2019-09-03 16:30:30",
        "plans": [
            {
                "id": 1,
                "product_id": 1,
                "price": "46.00",
                "type": "off",
                "created_at": "2019-09-03 16:30:30",
                "updated_at": "2019-09-03 16:30:30"
            },
            {
                "id": 2,
                "product_id": 1,
                "price": "50.00",
                "type": "on",
                "created_at": "2019-09-03 16:30:30",
                "updated_at": "2019-09-03 16:30:30"
            }
        ]
    }
]

虽然带有 whereDoesntHave 的查询确保其相关模型的 NONE 与查询条件匹配

return Product::whereDoesntHave('plans', function ($q) {
    $q->where('type', 'off');
})->with('plans')->get();

结果

[
    {
        "id": 2,
        "title": "A product with none of its plans off",
        "created_at": "2019-09-03 16:30:30",
        "updated_at": "2019-09-03 16:30:30",
        "plans": [
            {
                "id": 3,
                "product_id": 2,
                "price": "49.00",
                "type": "on",
                "created_at": "2019-09-03 16:30:30",
                "updated_at": "2019-09-03 16:30:30"
            },
            {
                "id": 4,
                "product_id": 2,
                "price": "93.00",
                "type": "on",
                "created_at": "2019-09-03 16:30:30",
                "updated_at": "2019-09-03 16:30:30"
            }
        ]
    }
]

希望对你有帮助