[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