MongoDB的聚合查询

MongoDB的聚合查询
 
Java代码    www.zzzyk.com  
MongoClient mongoClient = null;  
try {  
    mongoClient = new MongoClient("102.198.119.29", 27017);  
    DB db = mongoClient.getDB("syslog");  
    //设置Where条件  
    DBObject match = new BasicDBObject("$match", new BasicDBObject(  
            "DATE",  
            (new BasicDBObject("$gt", "2012-11-28 00:19:00")).append(  
                    "$lt", "2012-11-29 09:19:00")));  
 
    //设置分组字段  
    BasicDBObject groupFilters = new BasicDBObject("_id", "$PRIORITY");  
    //对分组字段统计行数  
    groupFilters.put("count", new BasicDBObject("$sum", 1));  
    BasicDBObject group = new BasicDBObject("$group", groupFilters);  
    //设置显示的字段集合  
 
    DBObject fields = new BasicDBObject("PRIORITY", 1);  
    fields.put("_id", "$PRIORITY");  
    DBObject project = new BasicDBObject("$project", fields);  
    AggregationOutput output = db.getCollection("messages").aggregate(  
            match, project, group);  
    System.out.println(output.getCommandResult());  
} catch (UnknownHostException e) {  
    e.printStackTrace();  
}  

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