mongdb group聚合操作

1、数据准备

[{"goods_id":1,"cat_id":4,"goods_name":"KD876","goods_number":1,"click_count":7,"shop_price":1388.00,"add_time":1240902890},{"goods_id":4,"cat_id":8,"goods_name":"u8bfau57fau4e9aN85u539fu88c5u5145u7535u5668","goods_number":17,"click_count":0,"shop_price":58.00,"add_time":1241422402},{"goods_id":3,"cat_id":8,"goods_name":"u8bfau57fau4e9au539fu88c55800u8033u673a","goods_number":24,"click_count":3,"shop_price":68.00,"add_time":1241422082},{"goods_id":5,"cat_id":11,"goods_name":"u7d22u7231u539fu88c5M2u5361u8bfbu5361u5668","goods_number":8,"click_count":3,"shop_price":20.00,"add_time":1241422518},{"goods_id":6,"cat_id":11,"goods_name":"u80dcu521bKINGMAXu5185u5b58u5361","goods_number":15,"click_count":0,"shop_price":42.00,"add_time":1241422573},{"goods_id":7,"cat_id":8,"goods_name":"u8bfau57fau4e9aN85u539fu88c5u7acbu4f53u58f0u8033u673aHS-82","goods_number":20,"click_count":0,"shop_price":100.00,"add_time":1241422785},{"goods_id":8,"cat_id":3,"goods_name":"u98deu5229u6d669@9v","goods_number":1,"click_count":9,"shop_price":399.00,"add_time":1241425512},{"goods_id":9,"cat_id":3,"goods_name":"u8bfau57fau4e9aE66","goods_number":4,"click_count":20,"shop_price":2298.00,"add_time":1241511871},{"goods_id":10,"cat_id":3,"goods_name":"u7d22u7231C702c","goods_number":7,"click_count":11,"shop_price":1328.00,"add_time":1241965622},{"goods_id":11,"cat_id":3,"goods_name":"u7d22u7231C702c","goods_number":1,"click_count":0,"shop_price":1300.00,"add_time":1241966951},{"goods_id":12,"cat_id":3,"goods_name":"u6469u6258u7f57u62c9A810","goods_number":8,"click_count":13,"shop_price":983.00,"add_time":1245297652}]

[{"goods_id":13,"cat_id":3,"goods_name":"u8bfau57fau4e9a5320 XpressMusic","goods_number":8,"click_count":13,"shop_price":1311.00,"add_time":1241967762},{"goods_id":14,"cat_id":4,"goods_name":"u8bfau57fau4e9a5800XM","goods_number":1,"click_count":6,"shop_price":2625.00,"add_time":1241968492},{"goods_id":15,"cat_id":3,"goods_name":"u6469u6258u7f57u62c9A810","goods_number":3,"click_count":8,"shop_price":788.00,"add_time":1241968703},{"goods_id":16,"cat_id":2,"goods_name":"u6052u57fau4f1fu4e1aG101","goods_number":0,"click_count":3,"shop_price":823.33,"add_time":1241968949},{"goods_id":17,"cat_id":3,"goods_name":"u590fu65b0N7","goods_number":1,"click_count":2,"shop_price":2300.00,"add_time":1241969394},{"goods_id":18,"cat_id":4,"goods_name":"u590fu65b0T5","goods_number":1,"click_count":0,"shop_price":2878.00,"add_time":1241969533},{"goods_id":19,"cat_id":3,"goods_name":"u4e09u661fSGH-F258","goods_number":12,"click_count":7,"shop_price":858.00,"add_time":1241970139},{"goods_id":20,"cat_id":3,"goods_name":"u4e09u661fBC01","goods_number":12,"click_count":14,"shop_price":280.00,"add_time":1241970417},{"goods_id":21,"cat_id":3,"goods_name":"u91d1u7acb A30","goods_number":40,"click_count":4,"shop_price":2000.00,"add_time":1241970634},{"goods_id":22,"cat_id":3,"goods_name":"u591au666eu8fbeTouch HD","goods_number":1,"click_count":15,"shop_price":5999.00,"add_time":1241971076}]

[{"goods_id":23,"cat_id":5,"goods_name":"u8bfau57fau4e9aN96","goods_number":8,"click_count":17,"shop_price":3700.00,"add_time":1241971488},{"goods_id":24,"cat_id":3,"goods_name":"P806","goods_number":100,"click_count":35,"shop_price":2000.00,"add_time":1241971981},{"goods_id":25,"cat_id":13,"goods_name":"u5c0fu7075u901a/u56fau8bdd50u5143u5145u503cu5361","goods_number":2,"click_count":0,"shop_price":48.00,"add_time":1241972709},{"goods_id":26,"cat_id":13,"goods_name":"u5c0fu7075u901a/u56fau8bdd20u5143u5145u503cu5361","goods_number":2,"click_count":0,"shop_price":19.00,"add_time":1241972789},{"goods_id":27,"cat_id":15,"goods_name":"u8054u901a100u5143u5145u503cu5361","goods_number":2,"click_count":0,"shop_price":95.00,"add_time":1241972894},{"goods_id":28,"cat_id":15,"goods_name":"u8054u901a50u5143u5145u503cu5361","goods_number":0,"click_count":0,"shop_price":45.00,"add_time":1241972976},{"goods_id":29,"cat_id":14,"goods_name":"u79fbu52a8100u5143u5145u503cu5361","goods_number":0,"click_count":0,"shop_price":90.00,"add_time":1241973022},{"goods_id":30,"cat_id":14,"goods_name":"u79fbu52a820u5143u5145u503cu5361","goods_number":9,"click_count":1,"shop_price":18.00,"add_time":1241973114},{"goods_id":31,"cat_id":3,"goods_name":"u6469u6258u7f57u62c9E8 ","goods_number":1,"click_count":5,"shop_price":1337.00,"add_time":1242110412},{"goods_id":32,"cat_id":3,"goods_name":"u8bfau57fau4e9aN85","goods_number":4,"click_count":9,"shop_price":3010.00,"add_time":1242110760}]

2、group参数解析

官方给出参数结构：

　　{
　　　　group:
　　　　　　{
　　　　　　　　ns: <namespace>,
　　　　　　　　key: <key>,
　　　　　　　　$reduce: <reduce function>,
　　　　　　　　$keyf: <key function>,
　　　　　　　　cond: <query>,
　　　　　　　　finalize: <finalize function>
　　　　　　}
　　}

重要参数解析：
　　key：作为分组的key
　　reduce：这些函数可以返回一个sum或count。该函数接受两个参数(curr,result)：curr(当前文档)和result(分组聚集的结果文档)。
　　initial：初始化聚合结果文档变量，为空时自动为每列提供初始变量。
　　keyf：可选。替代的key 字段。指定一个函数创建一个“key object”作为分组的key。使用keyf而是通过group by领域而不是现有的文档域键组。
　　cond：过滤条件
　　finalize：在db.collection.group()返回最终结果之前，此功能可以修改的结果文档或替换的结果文档作为一个整体。

3、执行顺序解析

1、key-->2、initial-->3、cond-->4、reduce   将本组信息存储，然后其他组循环2，3，4执行

4、执行案例

#key：表示分组的字段
#cond：分组后查询的条件
#reduce：聚合操作，其中curr表示当前文档的指针，result表示分组聚集的文档
#initial:参数初始化操作
#finalize:最终执行函数，类似java中的finally代码块

#查询每个栏目下的商品数量
{
key:{cat_id:1},  
cond:{},
reduce:function(curr,result) {
    result.cnt += 1;
},
initial:{cnt:0}
}


#查询每个栏目下价格高于50元的商品数量
{
key:{cat_id:1},
cond:{shop_price:{$gt:50}},
reduce:function(curr,res){
    res.cnt +=1;
},
initial:{cnt:0}
}

#每个栏目下的商品库存量 sum()操作
{
key:{cat_id:1},
cond:{},
reduce:function(curr,res){
    res.num +=curr.goods_number;
},
initial:{num:0}
}

#查询每个栏目最贵的商品价格, max()操作
{
key:{cat_id:1},
cond:{},
reduce:function(curr,res){
    if(res.price<curr.shop_price){
        res.price = curr.shop_price;
    }
},
initial:{price:0}
}

#查询每个栏目下商品的平均价格
{
key:{cat_id:1},
cond:{},
reduce:function(curr,res){
    res.cnt +=1;
    res.sum += curr.shop_price;

},
initial:{sum:0,cnt:0},
finalize:function(res){
    res.avg = res.sum/res.cnt;
}
}

　　

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