Question

是否可以根据最大值对数据进行排序。来自该组的价值。数据：

> db.test.find({})
{"a" : 1, "d" : 10 }
{"a" : 1, "d" : 1 }
{"a" : 2, "d" : 50 } // changed, it was initially ({"a" : 2, "d" : 20 })
{"a" : 2, "d" : 2 }
{"a" : 3, "d" : 30 }
{"a" : 3, "d" : 4 }
{"a" : 1, "d" : 10 }

结果：

a：2，d：50 | a：2：d：2 | a：3，d：30 | a：3，d：4 | a：1，d：10 | a：1，d：10 | a：1，d 1

SQL等价物：

create table test(a integer, d integer);
insert into test 
select 3,  30 union all
select 3,  4 union all
select 2,  20 union all
select 2,  2 union all
select 1, 10 union all
select 1,  10 union all
select 1, 1;

select a, d, max(d) over (partition by a) as max_in_group
from test
order by 3 desc, 2 desc;

或

select *
from test t
inner join 
(
select a, max ( d ) as max_d
from test
group by a
)X on t.a = x.a
order by max_d desc, d desc

感谢。

Answer 1

考虑使用aggregation framework：

db.coll.aggregate(
  {$sort: {d: -1}},
  {$group: {_id: "$a", d: {$push: "$d"}, max: {$max: "$d"}}},
  {$sort: {max: -1}},
  {$unwind: "$d"},
  {$project: {a: "$_id", d: 1, _id: false}}
);

结果：

{ "d" : 30, "a" : 3 }
{ "d" : 4,  "a" : 3 }
{ "d" : 20, "a" : 2 }
{ "d" : 2,  "a" : 2 }
{ "d" : 10, "a" : 1 }
{ "d" : 10, "a" : 1 }
{ "d" : 1,  "a" : 1 }

P.S。：如果您不在组内处理订单，您可以删除第一个管道阶段{$sort: {d: -1}};你会得到下一个结果：

{ "d" : 30, "a" : 3 }
{ "d" : 4,  "a" : 3 }
{ "d" : 20, "a" : 2 }
{ "d" : 2,  "a" : 2 }
{ "d" : 10, "a" : 1 } 
{ "d" : 1,  "a" : 1 } // <--   not
{ "d" : 10, "a" : 1 } // <-- ordered

MongoDB组和排序文档

1 个答案: