[Mysql] ORDER BY sort and retrieve data

Sorting query results is a very common requirement. We can use the ORDER BY clause to achieve the purpose The ORDER BY clause takes the name of one or more columns and sorts the output accordingly Typically, the columns used in the ORDER BY clause will be the columns selected for display. However, in fact, this is not necessary. It is complet ...

Posted by jbol on Sun, 24 Apr 2022 19:05:29 +0300

Linux Web publishing (Apache)

Install http server Download the source package http-2.425 Tar GZ as an example. (all images are on the home page) Configure IP first vim /etc/sysconfig/network-scripts/ifcfg-ens33 ((edit below) TYPE=Ethernet BOOTPROTO=none DEFROUTE=yes PEERDNS=yes PEERROUTES=yes IPV4 FAILURE FATAL=no IPV6INIT=yes IPV6 AUTOCONF=yes IPV6_DEFROUTE ...

Posted by TheOracle on Thu, 21 Apr 2022 18:55:17 +0300

13MySQL aggregate function

catalogue Introduction to aggregate function What is an aggregate function Aggregate function type Aggregate function syntax Aggregate functions cannot be nested calls. AVG / SUM: only applicable to fields (or variables) of numeric type Extension: String summation: 0 Order in MySQL directly reports invalid numbers MAX / MIN: applicable ...

Posted by Groogy on Tue, 19 Apr 2022 02:50:32 +0300

Joint index, overlay index and leftmost matching principle | MySQL index learning

The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.IntroductionIn the process of data retrieval, there are often matching requirements for multiple columns. Today, I will introduce the use of joint index and the case of the leftmost matching principle.The ...

Posted by itsjareds on Mon, 18 Apr 2022 11:43:12 +0300

How to automatically download, extract and install third-party libraries to a specified directory during CMAKE compilation

The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.IntroductionIn the daily development process, it is inevitable to use a third-party library or separate some libraries for additional storage. If the library and code are put together, it will inevitably c ...

Posted by sargus on Mon, 18 Apr 2022 11:03:03 +0300

Explore Presto SQL Engine - Analysis of Join

Author: vivo Internet technology Shuai GuangyingIn< Explore Presto SQL Engine (1) - skillfully use Antlr >In, we introduced the basic usage of Antlr and how to use Antlr4 to parse SQL query CSV data, and have a deeper understanding of the SQL syntax and implementation ideas supported by Presto query engine.This is the second in a series o ...

Posted by olsrey on Mon, 18 Apr 2022 06:39:59 +0300

Mysql database learning notes

Mysql database surface Table operationColumn operationTable data operationfunctionmulti-table query Indexes affair quarantine Storage engine view Administration user management Authority management Pictures are from Han Shunping Mysql When creating a database (without if not exists), the created inventory will report an error. The ...

Posted by Nic on Sun, 17 Apr 2022 21:23:58 +0300

Java backend pit entry record (updating...)

  Pit record MySQL pit record 1. Insert data times Unknown column 'Zhang San' in 'field list' -- Wrong way insert into `user`(`user_id`,`user_name`,`user_pwd`) values(3,`Wang Wu`,`wangwu`); -- Right way insert into `user`(`user_id`,`user_name`,`user_pwd`) values(3,'Wang Wu','wangwu'); Copy code Reason: for database name, table name and f ...

Posted by electrix on Sun, 17 Apr 2022 15:48:11 +0300

Table partition (horizontal) operation record 2 of SQLSERVER

1 ---- (non original, just sort out the records by yourself!!!)--------------- Original address: https://www.cnblogs.com/libingql/category/184251.html     1. Of course, many test data are needed to useGenerate test data. For example, I operate with 10000000 million data   1. It is applicable to the partition operation of existing data tables. O ...

Posted by yacaph on Sun, 17 Apr 2022 11:23:50 +0300

PostgreSQL learning summary -- PostgreSQL multi tenant analysis based on database and schema

Multi tenancy based on DATABASE 1. Advantages The way of database isolation is relatively complete, and there are few shared resources. Storage isolation can be realized; connection isolation can be realized; The isolation of auth can be realized; Permission isolation can be realized. Isolation starts from the authentication level, and there ...

Posted by markbm on Sat, 16 Apr 2022 00:06:43 +0300