文档查询
语法：
db.collectionName.find(query, projection);
//query ：可选，使用查询操作符指定查询条件
//projection：可选，使用投影操作符指定返回的键。
//默认省略，返回文档中所有键值。
//查询单条记录
db.collectionName.findOne(query, projection);
pretty() 方法可将结果格式化为可读模式
db.collectionName.find(query, projection).pretty();
query 条件
字段比较
| 操作 | 格式 | 示例 | 类比RDBMS |
|---|---|---|---|
| 等于 | {key:value} | {"CONTENT":"1"} | where CONTENT = '1' |
| 小于 | {key:{$lt:value}} | {"money":{$lt:50}} | where money < 50 |
| 小于或等于 | {key:{$lte:value}} | {"money":{$lte:50}} | where money <= 50 |
| 大于 | {key:{$gt:value}} | {"money":{$gt:50}} | where money > 50 |
| 大于或等于 | {key:{$gte:value}} | {"money":{$gte:50}} | where money >= 50 |
| 不等于 | {key:{$ne:value}} | {"money":{$ne:50}} | where money != 50 |
| 类型匹配 | {key:{$type:value}} | {"money":{$type:1}} | -- |
AND 条件
格式：
{key1:value1, key2:value2}
//示例 db.demo.find({"AUTOR" : "houxx","CONTENT" : "1"}).pretty();
OR 条件
格式：
{$or: [{key1: value1}, {key2:value2}]}
//示例
db.demo.find({$or: [{"CONTENT" : "1"}, {"CONTENT" : "2"}]},{_id:0}).pretty();
条件组合
直接把各个条件组合使用即可
示例：
//AUTOR 为 houxx ，且 money 的值等于1或大于2
db.demo.find({{"AUTOR":"houxx"},{$or: [{"money":1},{"money":{$gt:2}}]}},{_id:0}).pretty();
projection 条件
格式：
{字段名1:1,字段名2:1} // inclusion 模式，返回指定字段
{字段名1:0,字段名2:0} // exclusion 模式，指定字段不返回
//_id 键默认返回，需要主动指定 _id:0 才会隐藏
//两种模式不能混用，全 1 或全 0
$type 类型匹配
$type 取值
| value | 类型 |
|---|---|
| 1 | Double |
| 2 | String |
| 3 | Object |
| 4 | Array |
| 5 | Binary data |
| 6 | Undefined（已废弃） |
| 7 | Object id |
| 8 | Boolean |
| 9 | Date |
| 10 | Null |
| 11 | Regular Expression |
| 13 | JavaScript |
| 14 | Symbol |
| 15 | JavaScript (with scope) |
| 16 | 32-bit integer |
| 17 | Timestamp |
| 18 | 64-bit integer |
| 255 | Min key（写作 -1） |
| 127 | Max key |
示例：
//插入测试数据
> db.demo.insertMany([{"CONTENT":"1","AUTOR":"houxx"},{"CONTENT":"2","AUTOR":"houxx"},{"CONTENT":"1","AUTOR":"houxx"},{},{"CONTENT":"3","AUTOR":"houxx"}]);
{
"acknowledged" : true,
"insertedIds" : [
ObjectId("5b26327f2afff603f6bd2ca5"),
ObjectId("5b26327f2afff603f6bd2ca6"),
ObjectId("5b26327f2afff603f6bd2ca7"),
ObjectId("5b26327f2afff603f6bd2ca8"),
ObjectId("5b26327f2afff603f6bd2ca9")
]
}
//直接查找所有
> db.demo.find();
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca5"), "CONTENT" : "1", "AUTOR" : "houxx" }
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca6"), "CONTENT" : "2", "AUTOR" : "houxx" }
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca7"), "CONTENT" : "1", "AUTOR" : "houxx" }
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca8") }
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca9"), "CONTENT" : "3", "AUTOR" : "houxx" }
//查找所有格式化输出
> db.demo.find().pretty();
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca5"),
"CONTENT" : "1",
"AUTOR" : "houxx"
}
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca6"),
"CONTENT" : "2",
"AUTOR" : "houxx"
}
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca7"),
"CONTENT" : "1",
"AUTOR" : "houxx"
}
{ "_id" : ObjectId("5b26327f2afff603f6bd2ca8") }
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca9"),
"CONTENT" : "3",
"AUTOR" : "houxx"
}
//指定 _id 不返回
> db.demo.find({},{_id:0});
{ "CONTENT" : "1", "AUTOR" : "houxx" }
{ "CONTENT" : "2", "AUTOR" : "houxx" }
{ "CONTENT" : "1", "AUTOR" : "houxx" }
{ }
{ "CONTENT" : "3", "AUTOR" : "houxx" }
// AND 条件示例
> db.demo.find({"AUTOR" : "houxx","CONTENT" : "1"}).pretty();
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca5"),
"CONTENT" : "1",
"AUTOR" : "houxx"
}
{
"_id" : ObjectId("5b26327f2afff603f6bd2ca7"),
"CONTENT" : "1",
"AUTOR" : "houxx"
}
// OR 条件示例
> db.demo.find({$or: [{"CONTENT" : "1"}, {"CONTENT" : "2"}]},{_id:0}).pretty();
{ "CONTENT" : "1", "AUTOR" : "houxx" }
{ "CONTENT" : "2", "AUTOR" : "houxx" }
{ "CONTENT" : "1", "AUTOR" : "houxx" }
