修复了一些bug

Query.js

@@ -0,0 +1,52 @@
+// 房价均价查询语句
+
+db.lianjia.aggregate([
+    {'$match': {"address.0": {$exists: true}}},
+    {
+        $group: {
+            _id: {"$arrayElemAt": ["$address", 0]},
+            count: {$sum: 1},
+            avg_UnitPrice: {$avg: "$UnitPrice"},
+            std: {$stdDevPop: "$UnitPrice"},
+        }
+    },
+    {
+        $project:
+            {
+                count: 1,        //总数
+                avg_UnitPrice: 1, //每平米均价
+                std: 1,   //标准差
+                ratio: {$divide: ["$std", "$avg_UnitPrice"]} //标准差与均价的比值
+            }
+    },
+    {
+        '$sort': {count: -1}
+    }
+]);
+
+
+// 平均薪资查询语句
+
+db.zhilian.aggregate([
+    {'$match': {"workingExp.name": "1-3年"}},
+    {
+        $group: {
+            _id: {"$arrayElemAt": ["$city.items", 0]},
+            count: {$sum: 1},
+            avg: {$avg: "$avg"},
+            std: {$stdDevPop: "$avg"},
+        }
+    },
+    {
+        $project:
+            {
+                count: 1,   //总数
+                avg: 1, //平均薪资
+                std: 1,   //标准差
+                ratio: {$divide: ["$std", "$avg"]} //标准差与均价的比值
+            }
+    },
+    {
+        '$sort': {count: -1}
+    }
+]);