mysql - 如何在 Laravel 5.1 中编写这个(左连接，子查询)？

Question

如何在 Laravel 5.1 中编写此查询:

SELECT p.id, p.title, p.created_at, p.updated_at, u.name, COALESCE(c.comments_count, 0) AS comments_count, COALESCE(pl.status_sum, 0) AS status_sum

FROM posts p

LEFT OUTER JOIN users u ON u.id = p.user_id

LEFT OUTER JOIN (
    SELECT pl.post_id, SUM(pl.status) AS status_sum
    FROM postslikes pl
    GROUP BY pl.post_id
) pl ON pl.post_id = p.id

LEFT OUTER JOIN (
    SELECT c.post_id, COUNT(*) as comments_count
    FROM comments c
    GROUP BY c.post_id
) c ON c.post_id = p.id ORDER BY comments_count DESC

我需要它来进行分页。我可以毫无问题地执行这个原始查询，但是手动分页器总是给出相同的结果: http://laravel.com/docs/5.1/pagination#manually-creating-a-paginator与此处相同的问题:http://laravel.io/forum/07-22-2015-laravel-51-manual-pagination-not-working-as-expected

我的尝试没有成功:

DB::table( 'posts' )
    ->select( 'posts.id', 'posts.title', 'posts.created_at', 'posts.updated_at', 'users.name', DB::raw( 'COALESCE( comments.body, 0 ), COALESCE( postslikes.status, 0 )' ) )

    ->leftJoin( 'users', 'users.id', '=', 'posts.user_id' )

    ->leftJoin( DB::raw( 'SELECT postslikes.post_id, SUM( postslikes.status ) FROM postslikes GROUP BY postslikes.post_id' ), function( $join )
    {
        $join->on( 'postslikes.post_id', '=', 'post.id' );
    })

    ->leftJoin( DB::raw( 'SELECT comments.post_id, COUNT(*) FROM comments GROUP BY comments.post_id' ), function( $join )
    {
        $join->on( 'comments.post_id', '=', 'post.id' );
    })

    ->get();

我认为问题出在comments_count 和status_sum 上？谢谢!

Answer 1

要在 Laravel 的查询构建器中使用子查询，您应该按如下方式将其添加到连接中:

->leftJoin(DB::raw("(SELECT [...]) AS p"), 'p.post_id', '=', 'posts.id')

最好为计算字段创建一个别名，就像您在原始查询中所做的那样:

COUNT(*) AS count

尽管有这些变化，除非我错了，否则您可以从简化查询开始。以这种方式删除子查询:

SELECT
  p.id,
  p.title,
  p.created_at,
  p.updated_at,
  u.name,
  COUNT(c.id) AS comments_count,
  COALESCE(SUM(pl.status), 0) AS status_sum
FROM
  posts p
LEFT OUTER JOIN
  users u
ON 
  u.id = p.user_id
LEFT OUTER JOIN 
  postslikes pl
ON 
  pl.post_id = p.id
LEFT OUTER JOIN 
  comments c
ON 
  c.post_id = p.id 
ORDER BY 
  comments_count DESC
GROUP BY
  p.id

然后，有了这个新查询，您可以使用 Laravel 来构建它:

DB::table('posts')
  ->select([
    'posts.id',
    'posts.title',
    'posts.created_at',
    'posts.updated_at',
    'users.name',
    DB::raw('COUNT(comments.id) AS comments_count'),
    DB::raw('COALESCE(SUM(postslikes.status), 0) AS status_sum'),
  ])
  ->leftJoin('users', 'users.id', '=', 'posts.user_id')
  ->leftJoin('comments', 'comments.post_id', '=', 'posts.id')
  ->leftJoin('postslikes', 'postslikes.post_id', '=', 'posts.id')
  ->orderBy('comments_count', 'DESC')
  ->groupBy('posts.id')
  ->get();

请注意，我假设您的 comments 表中有一个名为 id 的列，它是主键。