Question

对于作业，我们会得到以下代码：

db.bib.insertMany( [
      {type : "book",
         "@year": "1994",
         "title": "TCP/IP Illustrated",
         "author": {
            "last": "Stevens",
            "first": "W."
         },
         "publisher": "Addison-Wesley",
         "price": "65"
      },
      {type : "book",
         "@year": "1992",
         "title": "Unix Programming",
         "author": {
            "last": "Stevens",
            "first": "W."
         },
         "publisher": "Addison-Wesley",
         "price": "65"
      },
      {type : "book",
         "@year": "2000",
         "title": "Data on the Web",
         "author": [
            {
               "last": "Abiteboul",
               "first": "Serge"
            },
            {
               "last": "Buneman",
               "first": "Peter"
            },
            {
               "last": "Suciu",
               "first": "Dan"
            }
         ],
         "publisher": "Morgan Kaufmann",
         "price": "39"
      },
      {type : "book",
         "@year": "1999",
         "title": "Digital TV",
         "editor": {
            "last": "Gerbarg",
            "first": "Darcy",
            "affiliation": "CITI"
         },
         "publisher": "Kluwer",
         "price": "130"
      }
    ,
      {type : "journal",
      "title": "Irreproducible results",
      "editor": {
         "last": "Self",
         "first": "W."
      },
      "publisher": "SV"
   }
])

使用mongoDB，我们会被要求完成不同的搜索查询，以便找到所需的信息。我目前坚持的那个是

列出1995年以后出版的书籍的标题，费用低于100.

根据我的理解，正确的查询应该是

db.bib.find({price: {$lt: 100}, year: {$gt: 1995}}, {title: 1, _id: 0})

但是，如果不这样做，则会提供空白结果。为什么这样，我该如何解决？

Answer 1

两个字段的数据类型都是字符串。你无法将它们作为数字进行比较。尝试以下，它会工作。使用排序规则，您可以要求MongoDB将它们视为int。您可以阅读有关排序规则here at mongodb.com的更多信息。

db.bib.find({$and: [{"@year": {$gt: "1995"}}, {price: {$lt: "100"}}]}).collation({
  locale: "en_US",
  numericOrdering: true
});

mongoDB搜索查询

1 个答案: