MongoDB等价于`collectionName中选择“ distinct(name)”，其中age =“ 25”？
您可以使用distinct()来获取选择distinct的等效项。首先让我们创建一个包含文档的集合-
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"John","Age":23});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd12759e3526dbddbbfb60b")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Larry","Age":25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd12768e3526dbddbbfb60c")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"David","Age":25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd12773e3526dbddbbfb60d")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Carol","Age":26});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd1277ee3526dbddbbfb60e")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Sam","Age":25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd12793e3526dbddbbfb60f")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Larry","Age":25});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd127a3e3526dbddbbfb610")
}
> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Carol","Age":26});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd127aae3526dbddbbfb611")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.distinctNameAndAgeDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd12759e3526dbddbbfb60b"),
"ClientFirstName" : "John",
"Age" : 23
}
{
"_id" : ObjectId("5cd12768e3526dbddbbfb60c"),
"ClientFirstName" : "Larry",
"Age" : 25
}
{
"_id" : ObjectId("5cd12773e3526dbddbbfb60d"),
"ClientFirstName" : "David",
"Age" : 25
}
{
"_id" : ObjectId("5cd1277ee3526dbddbbfb60e"),
"ClientFirstName" : "Carol",
"Age" : 26
}
{
"_id" : ObjectId("5cd12793e3526dbddbbfb60f"),
"ClientFirstName" : "Sam",
"Age" : 25
}
{
"_id" : ObjectId("5cd127a3e3526dbddbbfb610"),
"ClientFirstName" : "Larry",
"Age" : 25
}
{
"_id" : ObjectId("5cd127aae3526dbddbbfb611"),
"ClientFirstName" : "Carol",
"Age" : 26
}以下查询等效于`collectionName中的selectdifferent(name)，其中age=“25”-
> db.distinctNameAndAgeDemo.distinct("ClientFirstName", {"Age": 25});这将产生以下输出-
[ "Larry", "David", "Sam" ]
在上方，我们显示了年龄25岁的客户名称。
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