我如何获得此 SQL 查询？

Question

模型是：

Group {
    Id : int
}

Item {
    GroupId : int
    Status : int
}

如何查询此输出 table:

GroupID | TotalItemCount | ItemsWithStatus = 1 | ItemsWithStatus = 2

Answer 1

我怀疑你想要：

select g.groupid, count(*) as numitems,
       sum(case when i.status = 1 then 1 else 0 end) as status_1,
       sum(case when i.status = 2 then 1 else 0 end) as status_2
from items i join
     groups g
     on i.groupid = g.id
group by g.groupid;