blocks|key|3156719|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3156720|+db.collection.find({}，{_id:+1，姓名:+1，年龄:+1})|blockquote|3156721|3156722|3156723|要查找的第一个参数(谓词)是您的选择标准，例如|3156724|3156725|+db.collection.find({年龄：{$gte:+21}})|3156726|3156727|3156728|第二个限制了您检索的字段，因此对于每个21岁或以上的人的名字：|3156729|3156730|+db.collection.find({年龄：{$gte:+21}}，{姓名:+1})|3156731|3156732|3156733|字段选择器始终拉回_id，除非您特别将其关闭：|3156734|3156735|+db.collection.find({}，{_id:+0})|3156736|3156737|3156738|但是，默认情况下，Mongo不会检查字段是否存在。如果要选择某些字段，并且只匹配包含这些字段的结果，则需要使用：|3156739|3156740|+db.collection.find({年龄：{+$exists:+true+}+})|3156741|3156742|3156743|MongoDB网站对.find()函数有更详细的描述！|3156744|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|-4|4|5|6|1B|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|1C|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|1D|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|1E|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|1F|7|@]|8|@]|9|$]]|$1|H|3|-4|4|5|6|1G|7|@]|8|@]|9|$]]|$1|I|3|J|4|C|6|1H|7|@]|8|@]|9|$]]|$1|K|3|-4|4|5|6|1I|7|@]|8|@]|9|$]]|$1|L|3|-4|4|5|6|1J|7|@]|8|@]|9|$]]|$1|M|3|N|4|5|6|1K|7|@]|8|@]|9|$]]|$1|O|3|-4|4|5|6|1L|7|@]|8|@]|9|$]]|$1|P|3|Q|4|C|6|1M|7|@]|8|@]|9|$]]|$1|R|3|-4|4|5|6|1N|7|@]|8|@]|9|$]]|$1|S|3|-4|4|5|6|1O|7|@]|8|@]|9|$]]|$1|T|3|U|4|5|6|1P|7|@]|8|@]|9|$]]|$1|V|3|-4|4|5|6|1Q|7|@]|8|@]|9|$]]|$1|W|3|X|4|C|6|1R|7|@]|8|@]|9|$]]|$1|Y|3|-4|4|5|6|1S|7|@]|8|@]|9|$]]|$1|Z|3|-4|4|5|6|1T|7|@]|8|@]|9|$]]|$1|10|3|11|4|5|6|1U|7|@]|8|@]|9|$]]|$1|12|3|-4|4|5|6|1V|7|@]|8|@]|9|$]]|$1|13|3|14|4|C|6|1W|7|@]|8|@]|9|$]]|$1|15|3|-4|4|5|6|1X|7|@]|8|@]|9|$]]|$1|16|3|-4|4|5|6|1Y|7|@]|8|@]|9|$]]|$1|17|3|18|4|5|6|1Z|7|@]|8|@]|9|$]]|$1|19|3|-4|4|5|6|20|7|@]|8|@]|9|$]]]|1A|$]]

<blockquote>
 db.collection.find({}, {_id: 1, name: 1, age: 1})
</blockquote>

The first argument to find (the predicate) is your selection criteria, e.g.

<blockquote>
 db.collection.find({age: {$gte: 21}})
</blockquote>

The second limits the fields you retrieve, so for the names over everyone 21 or older:

<blockquote>
 db.collection.find({age: {$gte: 21}}, {name: 1})
</blockquote>

The field selector always pulls back _id unless you specifically turn it off:

<blockquote>
 db.collection.find({}, {_id: 0})
</blockquote>

However, Mongo will not check for field existence by default. If you want to select certain fields, and match only results that have those fields, you will want to use:

<blockquote>
 db.collection.find({ age: { $exists: true } })
</blockquote>

The MongoDB website has a more detailed description of the .find() function!

blocks|key|2942619|text|谢谢！，我用下面的代码修复了它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2942620|++++BasicDBObject+select+=+new+BasicDBObject();
++++select.put("id",+1);
++++select.put("name",+1);
++++select.put("age",+1);
++++collection.find(new+BasicDBObject(),+select);|code-block|syntax|javascript|2942621|上面的代码给了我所有的记录，只有上面的列名。|2942622|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Thanks!, I fixed it with the code below.

<pre><code> BasicDBObject select = new BasicDBObject();
 select.put("id", 1);
 select.put("name", 1);
 select.put("age", 1);
 collection.find(new BasicDBObject(), select);
</code></pre>

Above code gives me all the records, with only the column names as above.

blocks|key|3156797|text|如果您想选择一个或多个列，如SQL查询。例如，如果您的SQL查询如下|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3156798|select+name,+content+from+knowledgebase+where+applicationId='2955f3e174dce55190a87ed0e133adwdeb92';|code-block|syntax|javascript|3156799|MongoDB查询：|3156800|db.knowledgebase.find({+"applicationId":+"2955f3e174dce55190a87ed0e133adwdeb92"},+{+"name":+1,++++"content":+1});|3156801|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you want select one or multiple columns like SQL query. for example
if your SQL query like this 

<pre><code>select name, content from knowledgebase where applicationId='2955f3e174dce55190a87ed0e133adwdeb92';
</code></pre>

MongoDB query:

<pre><code>db.knowledgebase.find({ "applicationId": "2955f3e174dce55190a87ed0e133adwdeb92"}, { "name": 1, "content": 1});
</code></pre>

From my MongoDB I want the equivalent for

<pre><code> SELECT column1, column2
 FROM tbl
</code></pre>

With this code I get all the 'rows' but also all the 'columns'

<pre><code> DBCollection collection = database.getCollection("names");
 DBCursor cursor = collection.find();
</code></pre>

I for example would like all the 'rows' but only the 'columns': id, name, age 

How would I do this?

Thanks for any help!!

MongoDB Database, equivalent for SELECT column1, column2 FROM tbl

MongoDB

在我的MongoDB中，我想要等同于  SELECT column1, column2  FROM tbl使用这段代码，我得到了所有的“行”和所有的“列”。  DBCollection collection = database.getCollection("names");  DBCursor cursor = co...

问MongoDB数据库，等同于SELECT column1、column2 FROM tbl
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