Tag：Group
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Time：2020-2-21
28 this historic moment!!! Our team members started the first meeting of the project team in victor. Here’s a moment of meeting content~ 1. Everyone brainstormed, put forward a suggestion, denied, and finally, inspired by “forest” software, decided to make an app to help you run, clock in and add “appointment” function!!! 2. After […]
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Time：2020-2-19
1. count： Copy codeThe code is as follows: — in an empty collection, count returns 0. > db.test.count() 0— test the return value of count after inserting a document. > db.test.insert({“test”:1}) > db.test.count() 1 > db.test.insert({“test”:2}) > db.test.count() 2— count, like find, accepts conditions. From the results, […]
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Time：2020-1-31
I have created a goods table here. First, look at the data in it: mysql> select * from goods; +—-+——+——+————+————-+————+ | id | s_id | b_id | goods_name | goods_price | goods_desc | +—-+——+——+————+————-+————+ | 1 | 1 | 5 | book | 22.35 | book | | 2 | 2 | 5 | ball […]
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Time：2020-1-17
//Prepare test data db.user.drop(); for(var i=10; i< 100; i++) { db.user.insert({ name:”user” + i, age : Math.floor(Math.random()*10)+ 20, sex : Math.floor(Math.random()*3)%2 ==0 ? ‘M’ : ‘F’, chinese : Math.floor(Math.random()*50)+50, math : Math.floor(Math.random()*50)+50, english : Math.floor(Math.random()*50)+50, class : “C” + i%5 }) } //Group function //Group by class and display the user name and gender in […]
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Time：2020-1-12
Preface Among the new features of redis 5, the introduction of streams data structure can be said to be the biggest feature in this iteration. It enables redis to be used as a message queue in this iteration of version 5. X with more complete and powerful native support, especially the persistent message queue. At […]
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Time：2020-1-3
Creators do what they like to do and share with others, and get sponsorship from supporters to ensure sustainable output. This is a better way of collaboration than knowledge payment.Overseas platforms that can provide sponsorship function include patreon, and there are many excellent 5% service fee platforms in China. There are even technology flows that […]
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Time：2019-12-19
In the previous article, we introduced the detailed explanation of the data aggregation method implemented by MapReduce in mongodb. We mentioned a way of data aggregation operation in mongodb – MapReduce, but in most daily use processes, we do not need to use MapReduce for operation. In this article, we will briefly talk about the […]
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Time：2019-12-16
What is FISCO bcos generators FISCO bcos generator is an enterprise blockchain deployment tool for multi organization networking, which is suitable for multi organization deployment and maintenance of multi group alliance chain. 1.1 problems faced by enterprise deployment In the previous article, we introduced the build chain.sh script that can complete the blockchain deployment […]
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Time：2019-12-13
In English, order by means of row sorting, which is ascending by default. The sorted field names must be listed after order by, which can be multiple field names. Group by means of English. There must be an aggregate function to work with. At least one grouping flag field is required. What is aggregate function? […]
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Time：2019-12-5
We have introduced the overall framework of Kafka. Where is the final flow of Kafka producers’ messages? Of course, we need to consume. If we compare Kafka to a restaurant, then the producer is the chef, the consumer is the guest, and the chef is the only one, so it’s meaningless that no one eats […]
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Time：2019-12-2
1. System information arch #Display the processor architecture of the machine (1) uname -m #Display the processor architecture of the machine (2) uname -r #Show the kernel version in use dmidecode -q #Display hardware system components – (SMBIOS / DMI) hdparm -i /dev/hda #List the architecture features of a disk hdparm -tT /dev/sda #Performing a […]
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Time：2019-10-16
Now many enterprises and companies use network monitoring software to monitor the status of the server when they manage the server. Most of them use SNMP protocol (Simple Network Management Protocol) for monitoring. Then we need to open this service and make simple settings on our server side. The following is how to start and […]
