Question

您将如何在Ecto中编写相关子查询？

例如，什么是SQL SELECT查询的等价物：

--Heaviest Lemmings per Group
SELECT ld.group_name, ld.id, ld.name, ld.weight
FROM lemming_data ld
WHERE weight = (
    SELECT max(weight)
    FROM lemming_data
    WHERE group = ld.group_name
);

Ecto语法中的

？我不确定如何引用外部查询的group_name。

Answer 1

在不使用片段的情况下，Ecto中无法进行相关的子查询。所以它会是这样的：

$results = select(
          DB::raw("
                    pos_sales_code,
                    customer.customer_group,
                    customer_id,
                    customer.name,
                    customer.phone,
                    customer.email,
                    customer.referral_type AS referral,
                    pos_sales.created_at  AS first_visit,
                    pos_sales_product.product_name
                    "))
            ->join(DB::raw('SELECT customer_id, Min(created_at) AS first_visit
                           FROM   pos_sales
                           GROUP  BY customer_id) X'), function($join){

                   $join->on('post_sales.customer_id', '=', 'first_visit'));
                   $join->on('post_sales.created_at', '=',  'first_visit'));
                   })

            ->leftJoin('customer', 'customer.id', '=', 'pos_sales.customer_id')
            ->leftJoin('post_sales_product', 'pos_sales.pos_sales_code', '=', 'pos_sales_product.pos_sales_code')

            ->get();

或：

from ld in "lemming_data",
  where: ld.weight in fragment("(SELECT max(weight) FROM lemming_data WHERE group = ?)", ld.group_name),
  select: ld # or {ld.group_name, ld.id, ld.name, ld.weight}

使用Ecto的相关子查询

1 个答案: