如何从 MongoDB 集合中获取唯一值?
mongodbdatabasebig data analytics
要获取唯一值并忽略重复项，请在 MongoDB 中使用 distinct() 函数。distinct() 函数会查找单个集合中指定字段的不同值，并将结果以数组形式返回。
让我们创建一个包含文档的集合。
> db.demo704.insertOne({"LanguageCode":"hi"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee18551299a9f98c93bd")
}
> db.demo704.insertOne({"LanguageCode":"en"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee1e551299a9f98c93be")
}
> db.demo704.insertOne({"LanguageCode":"hi"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee20551299a9f98c93bf")
}
> db.demo704.insertOne({"LanguageCode":"eo"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee2c551299a9f98c93c0")
}
> db.demo704.insertOne({"LanguageCode":"eu"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee2f551299a9f98c93c1")
}
> db.demo704.insertOne({"LanguageCode":"fo"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee35551299a9f98c93c2")
}
> db.demo704.insertOne({"LanguageCode":"fo"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea6ee37551299a9f98c93c3")
}
借助 find() 方法显示集合中的所有文档 −
> db.demo704.find();
这将产生以下输出 −
{ "_id" : ObjectId("5ea6ee18551299a9f98c93bd"), "LanguageCode" : "hi" }
{ "_id" : ObjectId("5ea6ee1e551299a9f98c93be"), "LanguageCode" : "en" }
{ "_id" : ObjectId("5ea6ee20551299a9f98c93bf"), "LanguageCode" : "hi" }
{ "_id" : ObjectId("5ea6ee2c551299a9f98c93c0"), "LanguageCode" : "eo" }
{ "_id" : ObjectId("5ea6ee2f551299a9f98c93c1"), "LanguageCode" : "eu" }
{ "_id" : ObjectId("5ea6ee35551299a9f98c93c2"), "LanguageCode" : "fo" }
{ "_id" : ObjectId("5ea6ee37551299a9f98c93c3"), "LanguageCode" : "fo" }
以下查询用于获取唯一值并将结果显示在数组中 −
> db.demo704.distinct("LanguageCode");
这将产生以下输出 −
[ "hi", "en", "eo", "eu", "fo" ]
