如果觉得 Mongodb 语句不太好理解，可以和 SQL 语句进行对比，学起来要容易很多。
查询(find)
查询所有结果
select * from article db.article.find()
指定返回哪些键
select title, author from article
db.article.find({}, {"title": 1, "author": 1})where条件
select * from article where title = "mongodb"
db.article.find({"title": "mongodb"})and条件
select * from article where title = "mongodb" and author = "god"
db.article.find({"title": "mongodb", "author": "god"})or条件
select * from article where title = "mongodb" or author = "god"
db.article.find({"$or": [{"title": "mongodb"}, {"author": "god"}]})比较条件
select * from article where read >= 100;
db.article.find({"read": {"$gt": 100}})
> $gt(>)、$gte(>=)、$lt(<)、$lte(<=)
select * from article where read >= 100 and read <= 200
db.article.find({"read": {"$gte": 100, "lte": 200}})in条件
select * from article where author in ("a", "b", "c")
db.article.find({"author": {"$in": ["a", "b", "c"]}})like
select * from article where title like "%mongodb%"
db.article.find({"title": /mongodb/})count
select count(*) from article db.article.count()
不等于
select * from article where author != "a"
db.article.find({ "author": { "$ne": "a" }})
