Difference between revisions of "FIND Tutorial"

Revision as of 17:22, 13 November 2015

Working with the `world` collection of countries

This tutorial introduces NoSQL using MonogDB and PyMongo under Python3.4. We will be using the find() command and comparison functions on the collection world which contains details of around 250 countries of the world:

FIND examples are available.

Show Germany

Use find() to show the details of Germany

Show Germany instead of France

db.world.find({name:'France'})

db.world.find({name:'Germany'})

Eurasia - is that even a thing?

You can use .pretty() to make the output more readable.

List all the countries in the continent of "Eurasia"

db.world.find({name:'Germany'}).pretty()

db.world.find({continent:"Eurasia"}).pretty()

Find an area

You can test numbers as well as strings

Find the country with an area of exactly 43094

db.world.find({gdp:3425956000000}).pretty()

db.world.find({area:43094}).pretty()

Using $gt

You can use $gt and $lt to compare numbers and strings ($gt is greater than, $lt is less than)

Show each country with a population of over 250000000

db.world.find(
    {area:{$gt:9000000}},
    {name:1,_id:0}
).pretty()

db.world.find({population:{$gt:250000000}},{name:1,_id:0}).pretty()

After S

List the countries in Europe that come after "S" in the alphabet

 db.world.find({population:{$gt:80000000},
                continent:"Europe"},
               {name:1, _id:0})

Name and Capital

Find the name and capital cities for countries with a population of over 70 million

db.world.find(

   {population:{$gt:70000000}},
   {name:1,capital:1,_id:0}

).pretty()

Using $or

Find the countries that have a population of over 100 million or less than a million

db.world.find({$or:[{name:'Germany'},
                    {name:'France'}]},
              {name:1,population:1,_id:0})

db.world.find({$or:[{population:{$lt:1000000}},

                   {population:{$gt:100000000}}]},
             {name:1, population:1, _id:0})))

Find the names of countries beginning with "U" that are outside of Europe and North America

pp.pprint(list(db.world.find({"$and":[{"name":{'$regex':"^U"}},{"continent":{"$nin":["Europe", "North America"]}}]},{"name":1,"_id":0})))

Find the names of all countries that contain a white space

pp.pprint(list(db.world.find({"name":{"$regex":"^.*\s.*$"}},{"name":1,"_id":0})))

Which country out of China, Russia, and the United States has the largest population.

You might want to use Sort and limit to get the answer.

pp.pprint(list(db.world.find({"name":{"$in":["China", "Russia", "United States"]}}).sort("population",-1).limit(1)))

Use Sort to find the last document in world

Show the last document of world

pp.pprint(list(db.world.find().sort("$natural", -1))[0])

Show capital and population for the top 5 capital cities starting with the letter "M" that have a population of less than 3 million

pp.pprint(list(db.world.find({"$and":[{"capital":{"$regex":"^M"}},{"population":{"$lt":3000000}}]}, {"_id":0, "capital":1, "population":1}).sort("population",-1).limit(5)))

Show all the capitals for countries that start with the same letter as their continent

 find({"$where": " boolean expression "})

pp.pprint(list(

   db.world.find(
     {"$where":"this.name[0]==this.continent[0]"}, 
     {"_id":0, "capital":1})

))

@@ Line 72: / Line 72: @@
 </pre>
 <div class=ans>
-pp.pprint(list(db.world.find({population:{$gt:70000000}},{capital:1,name:1,_id:0})))
+db.world.find(
+    {population:{$gt:70000000}},
+    {name:1,capital:1,_id:0}
+).pretty()
 </div>
 </div>
-<div class=q data-lang="py3">
+==Using $or==
+<div class=q data-lang=mongo>
 <p class=strong>Find the countries that have a population of over 100 million or less than a million</p>
 <pre class=def>
+db.world.find({$or:[{name:'Germany'},
+                    {name:'France'}]},
+              {name:1,population:1,_id:0})
 </pre>
 <div class=ans>
-pp.pprint(list(db.world.find({"$or":[{"population":{"$lt":1000000}},{"population":{"$gt":100000000}}]}, {"name":1, "_id":0})))
+db.world.find({$or:[{population:{$lt:1000000}},
+                    {population:{$gt:100000000}}]},
+              {name:1, population:1, _id:0})))
 </div>
 </div>
-<div class=q data-lang="py3">
+<div class=q data-lang=mongo>
 <p class=strong>Find the names of countries beginning with "U" that are outside of Europe and North America</p>
 <pre class=def>