c# - SQL 到 LINQ。LEFT OUTER JOIN 和 GROUP BY 一起

Question

我有表“客户”和列“ID”、“国家”、“性别”。我想要的是在同一个查询中获得按国家字段分组的客户总数和男性和女性总数。我已经在sql查询中完成了。有用。但找不到如何在 LINQ 中实现它。

SELECT  c.country, COUNT(c.id) AS TotalClients, 
ISNULL(max(c2.total),0) AS TotalMales,
COUNT(c.id)-ISNULL(MAX(c2.total),0) AS TotalFemails,

FROM Clients c
LEFT OUTER JOIN(
SELECT country, count(id) AS total FROM Clients 
WHERE sex='male'
GROUP BY country
) c2 
ON c2.country = c.country
GROUP BY c.country
ORDER BY c.country

有什么建议么？

Answer 1

var query = (from c in db.Clients
            let TotalMales = (
            from c2 in db.Clients.Where(a=>a.Sex=='male') where c.Country=c2.Country select c2).Count()
            group c by new {c.Country, TotalMales}
            into g
            select new {
                g.Key.Country,
                TotalClients = g.Count(),
                TotalMales = g.Key.TotalMales,
                TotalFemales = g.Count()-TotalMales
            }).OrderBy(s=>s.Country);

Answer 2

考虑使用更简单的查询：

SELECT
  c.Country,
  SUM(CASE WHEN c.Sex = 'Male' THEN 1 ELSE 0 END) as TotalMales,
  SUM(CASE WHEN c.Sex = 'Female' THEN 1 ELSE 0 END) as TotalFemales,
  COUNT(*) as TotalClients
FROM Clients c
GROUP BY c.Country
ORDER BY c.Country

大致翻译为：

from c in Clients
group c by c.Country into g
order by g.Key
select new {
  Country = g.Key,
  Males = g.Count(y => y.Sex == "Male"),
  Females = g.Count(x => x.Sex == "Female"),
  Total = g.Count()
}