Supplementary record of sql basic syntax (to be continued 8 / 25)
I haven't done this for a long time. By the way, I was asked about it during the interview
1, distinct
1) Function
Remove duplicate items
2) Grammar
select distinct Column name from Table name;
give an example
Before use:(Here you can see that 3 repeat)
select client ID from Orders;
After use:(It can be seen here that onl ...
Posted by dlebowski on Thu, 25 Aug 2022 12:39:11 +0300
MySQL advanced - six index optimization
Database optimization scheme
Index failure, insufficient use of index: index establishmentToo many JOIN (design defects or unavoidable requirements) associated queries: SQL optimizationToo much data: sub database and sub tableServer tuning / optimization and various parameter settings (buffer, number of threads, etc.): adjust my.cnf
Performan ...
Posted by tanita on Sat, 06 Aug 2022 21:43:39 +0300
JDBC operation data and DAO design pattern in actual combat
Using JDBC to manipulate data
1. Using JDBC to write large text data to the database
Purpose: to java and other text files are written to the corresponding fields of the corresponding table by connecting the database with JDBC.
1. Table structure
2. Documents
3. Implementation code for inserting text
package LoadFileTest;
import driver.JDB ...
Posted by schoi on Wed, 25 May 2022 18:54:45 +0300
MySql advanced master-slave synchronization ☆
Master slave synchronization of MySql advanced
1. Replication overview
This means that the master and slave databases can be synchronized again by transferring these data to the master and slave databases through the DDL.
MySQL supports the replication of one master database to multiple slave databases at the same time. The slave database ca ...
Posted by upit on Wed, 25 May 2022 17:55:35 +0300
Database: mysql:undo log
1, Definition
Files required for transaction rollback.
2, Function
Rollback the transaction
MVCC control: when a user reads a row of record, if the record has been occupied by other transactions, the current transaction can read the previous row version information through undo log, so as to realize consistent non locking reading.
The snapsho ...
Posted by itsjareds on Wed, 25 May 2022 13:51:44 +0300
plsql, cursor, stored procedure
The following are personal study notes
The plsql language is case insensitive.
1. Program structure:
Plsql is divided into three parts: declaration part, executable part and exception handling part. Syntax:
declare
--Declaring variables, cursors
i integer;
begin
--Execute statement
--exception handling
end;
Example: print hello world ...
Posted by bnmng on Wed, 25 May 2022 12:34:32 +0300
Meituan distributed ID generator (Leaf), which can't be missed, is an easy-to-use batch
Leaf
Leaf is a distributed ID generation service launched by meituan. Its name is taken from the words of German philosopher and mathematician Leibniz: "there are no two identity leaves in the world." ("there are no two same leaves in the world"), taking a name has such moral meaning, meituan programmer Niu break!
Advantag ...
Posted by Chris_Evans on Wed, 25 May 2022 07:06:18 +0300
[Study Notes] Alibaba Cloud Tianchi Dragon Ball Project SQL Training Camp - Task03: Complex Query Methods - Views, Subqueries, Functions, etc.
s
This note is the learning content of Alibaba Cloud Tianchi Dragon Ball Project SQL Training Camp
The link is: https://tianchi.aliyun.com/specials/promotion/aicampsql
Practice Questions - Part 1
3.1
Create a view that satisfies the following three conditions (the view name is ViewPractice5_1). Using the product table as a referen ...
Posted by [e]r!k on Wed, 25 May 2022 06:53:14 +0300
[CRM learning and development Day1 of SSM framework project customer relationship management system]
1.1 home page function
demand
When users visit the project home page, they first enter the login page.
Timing & flow
IndexController
@Controller
public class IndexController {
/*
Theoretically, assign a url to the Controller method: http://127.0.0.1:8080/crm/
For simplicity, the protocol: / / ip:port / application ...
Posted by goldfiles on Wed, 25 May 2022 00:07:31 +0300
Filters, listeners and mysql
review
EL
Syntax ${expression}
EL domain objects, and lookup rules
pageScope
requestScope
sessionScope
applicationScope
What is the function of pageContext object in EL
You can get other objects
${ pageContext.request.contextPath }
How does EL display the attributes of students, elements in list and elements in map
${Student object. Pro ...
Posted by konqest on Mon, 23 May 2022 01:54:54 +0300