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法律學比較 2 個欄位的 MongoDB 查詢條件是什麼？
若要查詢比較 2 個欄位的條件，請使用以下語法 −
db.yourCollectionName.find( { $where: function() { return this.yourFirstFieldName < this.yourSecondFieldName } } ).pretty();為了理解此語法，我們建立一個文件集合。建立文件集合的查詢如下 −
> 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() 方法顯示集合中的所有文件。查詢如下
> db.comparingTwoFieldsDemo.find().pretty();
輸出如下 −
{
"_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
}以下是比較 2 個欄位的條件查詢 −
> db.comparingTwoFieldsDemo.find( { $where: function() { return this.StudentMathMarks < this.StudentPhysicsMarks } } ).pretty();輸出如下 −
{
"_id" : ObjectId("5c8ac0b46cea1f28b7aa0808"),
"StudentName" : "Carol",
"StudentAge" : 22,
"StudentMathMarks" : 79,
"StudentPhysicsMarks" : 89
}
{
"_id" : ObjectId("5c8ac0c96cea1f28b7aa0809"),
"StudentName" : "David",
"StudentAge" : 24,
"StudentMathMarks" : 39,
"StudentPhysicsMarks" : 45
}
更新於： 30-Jul-2019
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