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. Have you enjoyed the National Day? If you have a good time, you can deduct 1 from your brother Meng's comments and 2 from your brother Meng's comments. I hope to see everyone deduct 1 yo. If you think this article is helpful to you, you can give a hot article for three consecutive times. 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