Relational database standard language SQL
Summarized from database principle and application (MySQL Edition) Tsinghua University Press
#In syntax, [] indicates that this part is optional, < > indicates that this part is required, and is not written when writing specific commands, # as a single line comment, / * * / multiple lines
1, Data definition
1. Create database
CREATE ...
Posted on Sat, 09 Oct 2021 06:00:12 -0400 by pastcow
Descs of several table views commonly used in Oracle
1.1 dba_ start
dba_users Database user information dba_segments Table segment information dba_extents Data area information dba_objects Dat ...
Posted on Sat, 09 Oct 2021 03:07:08 -0400 by lettie
SQL function of ClickHouse and Update and Delete operations
1.SQL function
1.1 type detection function
toTypeName
select toTypeName(0); -- UInt8
select toTypeName(-0); -- UInt8
select toTypeName(1000); -- UInt16
select toTypeName(-1000); -- Int16
select toTypeName(10000000); -- UInt32
select toTypeName(-10000000); -- Int32
select toTypeName(1.99); -- Float64
select toTypeName(toFloat32(1.99)); ...
Posted on Fri, 08 Oct 2021 23:21:43 -0400 by mattcairns
MySQL deletes the data of the first three months of the data table
testrecord database stores player behavior records, which need to be cleaned up every three months.
Preparation before deleting data
To view the size of the testrecord database:
MySQL [(none)]> USE information_schema;
Database changed
MySQL [information_schema]> SELECT CONCAT(ROUND(SUM(DATA_LENGTH/1024/1024/1024),2),'GB')
-> a ...
Posted on Thu, 07 Oct 2021 17:15:58 -0400 by shortysbest
Look along the Hubble and see the overall architecture of MyBatis
1, Foreword
MyBatis is a very popular ORM framework at present. Its function is very powerful, but its implementation is relatively simple and elegant. This paper mainly describes the architecture design idea of MyBatis, discusses several core components of MyBatis, and then explores the implementation of MyBatis by combining a select quer ...
Posted on Thu, 07 Oct 2021 02:14:27 -0400 by everogrin
Deeply analyze SQL and NoSQL databases and master mainstream databases [20000 word analysis]
Hello, I'm spicy.
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catalogue
Database advanced fe ...
Posted on Thu, 07 Oct 2021 00:04:36 -0400 by DESIGNGRAPHY
MySQL learning summary - DDL (data definition language summary)
All database learning summary articles are summarized according to the shangsilicon Valley video of station B, and the video links are as follows:
[https://www.bilibili.com/video/BV12b411K7Zu]
Data definition language is mainly used for Library and table management. CREATE keyword: CREATE Modify keyword: ALTER Delete keyword: DROP
1 ...
Posted on Wed, 06 Oct 2021 22:27:06 -0400 by miniu
SQL statement Basics
data typeDQL languageDML languageDDL languageDCL languageTCL languageNon foreign key constraintForeign key constraintForeign key policyDDL and DML add a littleMulti table query syntaxSubqueryaffairTransaction concurrency problemTransaction isolation levelView + stored procedureJDBC+sql injection + other
Installation: uninstall all mysql and ma ...
Posted on Wed, 06 Oct 2021 17:13:50 -0400 by le007
Use of Mysql index optimization trace tool index design principles how to select an appropriate index what is index push down why does range lookup Mysql not use index push down optimization?
preface
In the previous chapters, I only learned about the principles of using indexes and what indexes to use with the explain keyword. The next two chapters consider how to make better use of indexes.
Example table
drop table `employees`;
CREATE TABLE `employees` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(24) NOT NULL ...
Posted on Mon, 04 Oct 2021 20:44:10 -0400 by alco19357
3. MyBatis Loading Strategy and Comment Development
I. MyBatis Loading Policy
1. What is delayed loading?
Problem: Configuration and implementation of one-to-one, one-to-many, many-to-many relationships in Mybatis is achievable Object's associated query. Many times in the actual development process we don't always need to load user information before we have to load his order information. This ...
Posted on Mon, 04 Oct 2021 12:32:20 -0400 by cayman_d