性能 linq group by with count

Question

我有一个使用 linq 和 group by 表达式的方法：

public List<SerieVu> ListSeriesLesPlusVuesSemaine()
{
    DateTime dateIlYaSeptJours = DateTime.Now.AddDays(-7);

    var resultat =
    from uev in Query(uev => uev.userepivu_date > dateIlYaSeptJours)
    group uev by uev.Episode.Saison.Serie into pgroup
    let count = pgroup.Count()
    orderby count descending
    select new SerieVu() { nombreDeVus = count, Serie = pgroup.Key };

    return resultat.Take(7).ToList();
}

这个 linq 查询生成这个 SQL 查询：

SELECT TOP (7) [Project1].[C2]                        AS [C1],
               [Project1].[C1]                        AS [C2],
               [Project1].[serie_id]                  AS [serie_id],
               [Project1].[serie_image]               AS [serie_image],
               [Project1].[serie_image_thumb]         AS [serie_image_thumb],
               [Project1].[serie_format]              AS [serie_format],
               [Project1].[serie_motsclefs]           AS [serie_motsclefs],
               [Project1].[serie_statusproduction_id] AS [serie_statusproduction_id],
               [Project1].[serie_nom]                 AS [serie_nom],
               [Project1].[serie_nomvf]               AS [serie_nomvf],
               [Project1].[serie_synopsis]            AS [serie_synopsis],
               [Project1].[serie_syncthetvdb]         AS [serie_syncthetvdb],
               [Project1].[serie_dateajout]           AS [serie_dateajout],
               [Project1].[serie_datemiseajour]       AS [serie_datemiseajour],
               [Project1].[serie_actif]               AS [serie_actif],
               [Project1].[utilisateur_id]            AS [utilisateur_id],
               [Project1].[serie_francais]            AS [serie_francais]
FROM   (SELECT [GroupBy1].[A1]  AS [C1],
               [GroupBy1].[K1]  AS [serie_id],
               [GroupBy1].[K2]  AS [serie_image],
               [GroupBy1].[K3]  AS [serie_image_thumb],
               [GroupBy1].[K4]  AS [serie_format],
               [GroupBy1].[K5]  AS [serie_motsclefs],
               [GroupBy1].[K6]  AS [serie_statusproduction_id],
               [GroupBy1].[K7]  AS [serie_nom],
               [GroupBy1].[K8]  AS [serie_nomvf],
               [GroupBy1].[K9]  AS [serie_synopsis],
               [GroupBy1].[K10] AS [serie_syncthetvdb],
               [GroupBy1].[K11] AS [serie_dateajout],
               [GroupBy1].[K12] AS [serie_datemiseajour],
               [GroupBy1].[K13] AS [serie_actif],
               [GroupBy1].[K14] AS [utilisateur_id],
               [GroupBy1].[K15] AS [serie_francais],
               1                AS [C2]
        FROM   (SELECT [Extent4].[serie_id]                  AS [K1],
                       [Extent4].[serie_image]               AS [K2],
                       [Extent4].[serie_image_thumb]         AS [K3],
                       [Extent4].[serie_format]              AS [K4],
                       [Extent4].[serie_motsclefs]           AS [K5],
                       [Extent4].[serie_statusproduction_id] AS [K6],
                       [Extent4].[serie_nom]                 AS [K7],
                       [Extent4].[serie_nomvf]               AS [K8],
                       [Extent4].[serie_synopsis]            AS [K9],
                       [Extent4].[serie_syncthetvdb]         AS [K10],
                       [Extent4].[serie_dateajout]           AS [K11],
                       [Extent4].[serie_datemiseajour]       AS [K12],
                       [Extent4].[serie_actif]               AS [K13],
                       [Extent4].[utilisateur_id]            AS [K14],
                       [Extent4].[serie_francais]            AS [K15],
                       COUNT(1)                              AS [A1]
                FROM   [dbo].[UtilisateurEpisodeVu] AS [Extent1]
                       INNER JOIN [dbo].[Episode] AS [Extent2]
                         ON [Extent1].[episode_id] = [Extent2].[episode_id]
                       INNER JOIN [dbo].[Saison] AS [Extent3]
                         ON [Extent2].[saison_id] = [Extent3].[saison_id]
                       LEFT OUTER JOIN [dbo].[Serie] AS [Extent4]
                         ON [Extent3].[serie_id] = [Extent4].[serie_id]
                WHERE  [Extent1].[userepivu_date] > '2013-01-11T09:53:26' /* @p__linq__0 */
                GROUP  BY [Extent4].[serie_id],
                          [Extent4].[serie_image],
                          [Extent4].[serie_image_thumb],
                          [Extent4].[serie_format],
                          [Extent4].[serie_motsclefs],
                          [Extent4].[serie_statusproduction_id],
                          [Extent4].[serie_nom],
                          [Extent4].[serie_nomvf],
                          [Extent4].[serie_synopsis],
                          [Extent4].[serie_syncthetvdb],
                          [Extent4].[serie_dateajout],
                          [Extent4].[serie_datemiseajour],
                          [Extent4].[serie_actif],
                          [Extent4].[utilisateur_id],
                          [Extent4].[serie_francais]) AS [GroupBy1]) AS [Project1]
ORDER  BY [Project1].[C1] DESC

我的问题是如何提高这个查询的性能？在我网站的一个非常重要的页面上大约需要 6 秒。

感谢您的帮助

Answer 1

您可以从在数据库中创建一些索引开始 您应该将字段表单 where、order by 和 group by 放在索引中 您可能会通过在 userepivu_date 上创建索引来获得最大的性能改进，因为这个 WHERE [Extent1].[userepivu_date] > '2013-01-11T09:53:26' 将扫描你的整个桌子

在 SQL Server 上创建索引：

CREATE INDEX [indexname] ON Extent1 (userepivu_date)

Answer 2

我应该给出的第一个建议是查看执行计划并寻找瓶颈

那么，为什么要使用 LEFT OUTER JOIN 呢？

LEFT OUTER JOIN [dbo].[Serie] AS [Extent4]

不应该是内部连接吗（如果是这样，您的映射可能有问题）？ 我想它可能会通过阻止在连接过程中早期执行 where 子句来搞砸查询优化。

也许您可以尝试运行查询，将左外连接替换为内连接，看看是否有区别。 另外，同意@user1802430 ，如果userepivu_date上没有索引，你肯定需要放一个。

Answer 3

我找到了解决方案。我已经使用显式连接强制内部连接：

public List<SerieVu> ListSeriesLesPlusVuesSemaine()
{
    DateTime dateIlYaSeptJours = DateTime.Now.AddDays(-7);

    ObjectSet<UtilisateurEpisodeVu> UtilisateurEpisodeVuSet = _context.CreateObjectSet<UtilisateurEpisodeVu>();
    ObjectSet<Episode> EpisodeSet = _context.CreateObjectSet<Episode>();
    ObjectSet<Saison> SaisonSet = _context.CreateObjectSet<Saison>();
    ObjectSet<Serie> SerieSet = _context.CreateObjectSet<Serie>();

    var resultat =
    from uev in UtilisateurEpisodeVuSet.Include("Episode.Saison.Serie").Where(uev => uev.userepivu_date > dateIlYaSeptJours)
    join e in EpisodeSet on uev.episode_id equals e.episode_id
    join sai in SaisonSet on e.saison_id equals sai.saison_id
    join s in SerieSet on sai.serie_id equals s.serie_id
    group uev by s into pgroup
    let count = pgroup.Count()
    orderby count descending
    select new SerieVu() { nombreDeVus = count, Serie = pgroup.Key };

    return resultat.Take(7).ToList();
}

使用这种方法，linq 查询只生成内部连接；）感谢所有试图帮助我的人