Difference between revisions of "FIND Examples"
From NoSQLZoo
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By default, <code>find()</code> returns the entire contents of a collection. This is equivalent to <code>find({})</code> | By default, <code>find()</code> returns the entire contents of a collection. This is equivalent to <code>find({})</code> | ||
<p class="strong">Show all the documents in world</p> | <p class="strong">Show all the documents in world</p> | ||
| − | <pre class="def">db.world.find()</pre> | + | <pre class="def"><nowiki>db.world.find();</nowiki><</pre> |
</div> | </div> | ||
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It is also possible to just return the first document with <code>findOne()</code>. | It is also possible to just return the first document with <code>findOne()</code>. | ||
<p class="strong">Show the first document of world</p> | <p class="strong">Show the first document of world</p> | ||
| − | <pre class="def"><nowiki>db.world.findOne()</nowiki></pre> | + | <pre class="def"><nowiki>db.world.findOne();</nowiki></pre> |
</div> | </div> | ||
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<pre><nowiki>db.world.find().skip(49).limit(1)</nowiki></pre> | <pre><nowiki>db.world.find().skip(49).limit(1)</nowiki></pre> | ||
<p class="strong">Get the 50th document of world</p> | <p class="strong">Get the 50th document of world</p> | ||
| − | <pre class="def"><nowiki>db.world.find()[49]</nowiki></pre> | + | <pre class="def"><nowiki>db.world.find()[49];</nowiki></pre> |
</div> | </div> | ||
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<code>find()</code> can filter results if a document is used as an argument. | <code>find()</code> can filter results if a document is used as an argument. | ||
<p class="strong">Get all the data concerning france</p> | <p class="strong">Get all the data concerning france</p> | ||
| − | <pre class="def"><nowiki>db.world.findOne({"name":"France"})</nowiki></pre> | + | <pre class="def"><nowiki>db.world.findOne({"name":"France"});</nowiki></pre> |
</div> | </div> | ||
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This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false to be excluded from the results set.<br/> | This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false to be excluded from the results set.<br/> | ||
<p class="strong">Get the population of Germany</p> | <p class="strong">Get the population of Germany</p> | ||
| − | <pre class="def"><nowiki>db.world.findOne({"name":"Germany"},{"population":1,"_id":0})</nowiki></pre> | + | <pre class="def"><nowiki>db.world.findOne({"name": "Germany"},{"population": 1,"_id": 0});</nowiki></pre> |
</div> | </div> | ||
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</pre> | </pre> | ||
<p class="strong">List the countries with a population that's less than 1 million.</p> | <p class="strong">List the countries with a population that's less than 1 million.</p> | ||
| − | <pre class="def"><nowiki>db.world.find({"population": {"$lt": 1000000}}, {"name": 1,"_id": 0})</nowiki></pre> | + | <pre class="def"><nowiki>db.world.find({"population": {"$lt": 1000000}}, {"name": 1,"_id": 0});</nowiki></pre> |
</div> | </div> | ||
| Line 68: | Line 68: | ||
<nowiki> | <nowiki> | ||
AND (implicit) | AND (implicit) | ||
| − | db.<collection>.find({<first condition>,<second condition>}) | + | db.<collection>.find({<first condition>,<second condition>}); |
| − | db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}}) | + | db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}}); |
AND (explicit) | AND (explicit) | ||
| − | db.<collection>.find({"$and":[<first condition>,<second condition>]}) | + | db.<collection>.find({"$and":[<first condition>,<second condition>]}); |
| − | db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}) | + | db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}); |
OR | OR | ||
| − | db.<collection>.find({"$or":[<first condition>,<second condition>]}) | + | db.<collection>.find({"$or":[<first condition>,<second condition>]}); |
| − | db.world.find({"$or":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}) | + | db.world.find({"$or":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}); |
</nowiki> | </nowiki> | ||
</pre> | </pre> | ||
<p class="strong">Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area.</p> | <p class="strong">Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area.</p> | ||
| − | <pre class="def"><nowiki>db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})</nowiki></pre> | + | <pre class="def"><nowiki>db.world.find({"population": {"$lt": 1000000},"area": {"$gt": 200000}},{"name": 1,"_id": 0});</nowiki></pre> |
</div> | </div> | ||
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Lists can be used with <code>$in</code> and <code>$nin</code>: | Lists can be used with <code>$in</code> and <code>$nin</code>: | ||
<p class="strong">Find the continent of Brazil, the United Kingdom, and Ghana.</p> | <p class="strong">Find the continent of Brazil, the United Kingdom, and Ghana.</p> | ||
| − | <pre class="def"> | + | <pre class="def"><nowiki> |
| − | <nowiki> | ||
db.world.find( | db.world.find( | ||
{name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}}, | {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}}, | ||
{name: 1, continent: 1, _id: 0} | {name: 1, continent: 1, _id: 0} | ||
| − | ) | + | );</nowiki></pre> |
| − | </nowiki> | ||
| − | </pre> | ||
</div> | </div> | ||
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Pattern matching is possible with Regular Expressions (RegEx)<br/> | Pattern matching is possible with Regular Expressions (RegEx)<br/> | ||
<p class="strong">Show each country that begins with G</p> [https://no.sqlzoo.net/wiki/RegEx_Pattern_Matching Reference] | <p class="strong">Show each country that begins with G</p> [https://no.sqlzoo.net/wiki/RegEx_Pattern_Matching Reference] | ||
| − | <pre class="def"> | + | <pre class="def"><nowiki> |
| − | <nowiki> | ||
db.world.find( | db.world.find( | ||
{name: {$regex: /^G/}}, | {name: {$regex: /^G/}}, | ||
{name: 1, continent: 1, _id: 0} | {name: 1, continent: 1, _id: 0} | ||
| − | ) | + | );</nowiki></pre> |
| − | </nowiki> | ||
| − | </pre> | ||
</div> | </div> | ||
Revision as of 19:50, 21 June 2018
Contents
Introducing the world collection of countries
These examples introduce NoSQL using MongoDB. We will be using the find() command on the collection world:
By default, find() returns the entire contents of a collection. This is equivalent to find({})
Show all the documents in world
db.world.find();<
find and findOne
It is also possible to just return the first document with findOne().
Show the first document of world
db.world.findOne();
skip and limit
It is also possible to specify which document to find by its position.
You can achieve the same with skip() and limit()
db.world.find().skip(49).limit(1)
Get the 50th document of world
db.world.find()[49];
Querying
find() can filter results if a document is used as an argument.
Get all the data concerning france
db.world.findOne({"name":"France"});
Using a projection with find
By passing a second parameter to find() the output can be limited to certain field(s)
In this example 1 indicates "true" and 0 indicates "false"
A feature of MongoDB is the ObjectID or _id.
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be explicitly set to false to be excluded from the results set.
Get the population of Germany
db.world.findOne({"name": "Germany"},{"population": 1,"_id": 0});
Comparisons $eq $gt $gte $lte $ne
MongoDB also allows comparisons. Syntax:
Mongo | MySQL -------------- $eq | == $gt | > $gte | >= $lt | < $lte | <= $ne | !=, <> $in | IN $nin | NOT IN
List the countries with a population that's less than 1 million.
db.world.find({"population": {"$lt": 1000000}}, {"name": 1,"_id": 0});
Logical operations $and $or $not
It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example:
AND (implicit)
db.<collection>.find({<first condition>,<second condition>});
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}});
AND (explicit)
db.<collection>.find({"$and":[<first condition>,<second condition>]});
db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]});
OR
db.<collection>.find({"$or":[<first condition>,<second condition>]});
db.world.find({"$or":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]});
Find the countries with less than 1 million people, but over 200000km2 area.
db.world.find({"population": {"$lt": 1000000},"area": {"$gt": 200000}},{"name": 1,"_id": 0});
$in and $nin
Lists can be used with $in and $nin:
Find the continent of Brazil, the United Kingdom, and Ghana.
db.world.find(
{name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}},
{name: 1, continent: 1, _id: 0}
);
Regular Expressions
Pattern matching is possible with Regular Expressions (RegEx)
Show each country that begins with G
Referencedb.world.find(
{name: {$regex: /^G/}},
{name: 1, continent: 1, _id: 0}
);