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Aggregation framework Aggregation framework: just another way to query data in MongoDB. Aggregate operation placed in [] Aggregation framework syntax: in the form of pipes, where phases are executed in the order they are listed. MongoDB Aggregation Framework ($group) (calculate & reshape data) > mongodb query language (MQL) (filter ...

Introduction:   This article mainly explains how to install MariaDB / MySQL database on raspberry PI (raspberry pie) system. For image download, domain name resolution and time synchronization, please click   Alibaba open source mirror station 1, Update system Update the system you need to install by running the following comman ...

A strange index failure occurred some time ago. The actual situation is similar to the following: bill=# begin; BEGIN bill=*# create index idx_t1 on t1(id); CREATE INDEX bill=*# explain select * from t1 where id = 1; QUERY PLAN ---------------------------------------------------- Seq Scan on t1 (cost=0.00..25.88 rows=6 w ...

Write in front: This article is my study record. If there are mistakes, please point them out and correct them immediately DDL, DQL, DML and DCL will be written in four parts, and DQL will be written in this article. What is DQL? DQL: data query language, used to query data First, paste a table, and the following query contents will be us ...

1. Requirements id start_time end_time 1001 2021-12-01 08:08:05 2021-12-01 19:02:07 1002 2021-12-01 08:15:07 2021-12-01 19:05:10 1003 2021-12-01 09:10:20 2021-12-01 21:02:07 1005 2021-12-01 09:26:05 2021-12-01 19:52:15 1006 2021-12-01 10:08:05 2021-12-01 22:05:06 1004 2021-12-01 10:20:07 2021-12-01 18 ...

[you in the future, will thank you for your efforts today] two questions a day, one difficult and one easy, and make a little progress every day, which may directly lead to the success of an interview or the easy completion of the work, so as to promote and raise salary, marry Bai Fumei, come on! 🍅 Venue: data warehouse exchange group ✖️ CSDN ...

1. View the current mariadb version.   rpm -qa |grep mariadb   2. Uninstall the current old version of mariadb and delete the configuration file and directory (version 5.5 does not support dynamic columns).   rm -f /etc/my.cnf       rm -rf /var/lib/mysql/ 3. Add the yum source for mariadb 10.2 and refresh the yum source. vim /e ...

Handwritten database connection pool The returned is a shared with connection_ PTR object Key technical points MySQL database programming, singleton mode, queue container, C++11 multithreading programming, thread mutual exclusion, thread synchronous communication (mutex, conditional variables) and unique_lock, CAS based atomic shaping, ...

catalogue 1, Introduction to mysql index 1. The concept of index 2. Basic principles of index creation 3. Index creation and classification 1. General index 2. Unique index 3. Primary key index 4. Combined index (single column index and multi column index) 5. Full text index (FULLTEXT) 4. View index 5. Delete index 2, Introduction t ...

preface: Previous articles have combed the whole process from front to back in terms of call structure. This article analyzes the whole process from the perspective of actual combat call. Before it was abstract, now it is actual combat. 1. Example code The code is the same as before. I'll post it here again 1.1 provider public class Pro ...