从MongoDB中的列获取不同的值？
要从列中获取不同的值，请distinct()在MongoDB中使用。首先让我们创建一个包含文档的集合-
> db.demo128.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e30583d68e7f832db1a7f5d")
}
> db.demo128.insertOne({"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e30584068e7f832db1a7f5e")
}
> db.demo128.insertOne({"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e30584368e7f832db1a7f5f")
}
> db.demo128.insertOne({"Name":"Bob"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e30584668e7f832db1a7f60")
}
> db.demo128.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e30584c68e7f832db1a7f61")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo128.find();
这将产生以下输出-
{ "_id" : ObjectId("5e30583d68e7f832db1a7f5d"), "Name" : "Chris" }
{ "_id" : ObjectId("5e30584068e7f832db1a7f5e"), "Name" : "David" }
{ "_id" : ObjectId("5e30584368e7f832db1a7f5f"), "Name" : "David" }
{ "_id" : ObjectId("5e30584668e7f832db1a7f60"), "Name" : "Bob" }
{ "_id" : ObjectId("5e30584c68e7f832db1a7f61"), "Name" : "Chris" }以下是从MongoDB中的列获取不同值的查询-
> db.demo128.distinct("Name");这将产生以下输出-
[ "Chris", "David", "Bob" ]