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法律学比较 2 个字段的 MongoDB 查询条件是什么？
若要查询比较 2 个字段的条件，请使用以下语法 −
db.yourCollectionName.find( { $where: function() { return this.yourFirstFieldName < this.yourSecondFieldName } } ).pretty();为了理解此语法，我们创建一个文档集合。创建文档集合的查询如下 −
> db.comparingTwoFieldsDemo.insertOne({"StudentName":"John","StudentAge":21,"StudentMathMarks":99,"StudentPhysicsMarks":98});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ac09e6cea1f28b7aa0807")
}
> db.comparingTwoFieldsDemo.insertOne({"StudentName":"Carol","StudentAge":22,"StudentMathMarks":79,"StudentPhysicsMarks":89});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ac0b46cea1f28b7aa0808")
}
> db.comparingTwoFieldsDemo.insertOne({"StudentName":"David","StudentAge":24,"StudentMathMarks":39,"StudentPhysicsMarks":45});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ac0c96cea1f28b7aa0809")
}
> db.comparingTwoFieldsDemo.insertOne({"StudentName":"Bob","StudentAge":23,"StudentMathMarks":87,"StudentPhysicsMarks":78});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ac0e06cea1f28b7aa080a")
}使用 find() 方法显示集合中的所有文档。查询如下
> db.comparingTwoFieldsDemo.find().pretty();
输出如下 −
{
"_id" : ObjectId("5c8ac09e6cea1f28b7aa0807"),
"StudentName" : "John",
"StudentAge" : 21,
"StudentMathMarks" : 99,
"StudentPhysicsMarks" : 98
}
{
"_id" : ObjectId("5c8ac0b46cea1f28b7aa0808"),
"StudentName" : "Carol",
"StudentAge" : 22,
"StudentMathMarks" : 79,
"StudentPhysicsMarks" : 89
}
{
"_id" : ObjectId("5c8ac0c96cea1f28b7aa0809"),
"StudentName" : "David",
"StudentAge" : 24,
"StudentMathMarks" : 39,
"StudentPhysicsMarks" : 45
}
{
"_id" : ObjectId("5c8ac0e06cea1f28b7aa080a"),
"StudentName" : "Bob",
"StudentAge" : 23,
"StudentMathMarks" : 87,
"StudentPhysicsMarks" : 78
}以下是比较 2 个字段的条件查询 −
> db.comparingTwoFieldsDemo.find( { $where: function() { return this.StudentMathMarks < this.StudentPhysicsMarks } } ).pretty();输出如下 −
{
"_id" : ObjectId("5c8ac0b46cea1f28b7aa0808"),
"StudentName" : "Carol",
"StudentAge" : 22,
"StudentMathMarks" : 79,
"StudentPhysicsMarks" : 89
}
{
"_id" : ObjectId("5c8ac0c96cea1f28b7aa0809"),
"StudentName" : "David",
"StudentAge" : 24,
"StudentMathMarks" : 39,
"StudentPhysicsMarks" : 45
}
更新于： 30-Jul-2019
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