After one year of postgraduate entrance examination, I was brushed by Harbin University of Technology , Programming technology is a little delayed , I wanted to do project training directly , There are so many loopholes that I have to go through the basics .

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Preface

I can't go on with the project , A lot of basic knowledge has been forgotten , I'm going to study the route I learned before systematically .

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Tools and FAQs

dbeaver( It's said to be very convenient. I didn't try )
phpstudy ： Open and use （ I'm using this ）
navicat,sqlyog : General tools
Tip：

1. 5.7 The port number of the version is 13306 ;8.0 The version is 3306

2. This problem occurs because you don't open MySQL I have been asked this question since the experiment at school ！！！！

3. This is because the user name and password of your connection are incorrect .

4. This is just 8.0 Version will encounter this problem , Because of encryption rules and 5.7 The inconsistent . The solution is ①： Upgrade GUI tool version .②： Restore the encryption rules to 5.7 The appearance of

5. In addition, if the service cannot be started automatically, it may be because it is placed under the Chinese folder during installation , Or move the installed source path without permission .
   Then start now MySQL, What I use here is php Integrated environment

One 、 Non relational database

Relational database ： The set of relationships between entities constitutes a relational database .（ Multiple entities ）
Non relational database ： Collectively referred to as NoSQL

Two 、 Relational database design rules

notes

Alias

annual sal A space in the middle cannot be used as an overall alias , You need double quotes to use the whole as an alias

Remove duplicate lines ：DISTINCT

null

null Not at all 0
In the calculation, there is null The calculation results involved are null

mark of emphasis

The table with the same name as the keyword is marked with emphasis .

Display table structure

WHERE Filter conditions

WHERE Give priority to FROM Back

<=> Safety is equal to （ by null born ）

Safety equals and ordinary equals are different

Operator

like Fuzzy query

Sorting and paging

Default ascending order

Column aliases can only be used in ORDER BY Use in , Can't be in WHERE Use in

WHERE and ORDER BY The order of

Pagination

When querying a database, there are a large number of databases , Pagination is more humanized
LIMIT： LIMIT 10 It means LIMIT 0,10 , Indicates that ten records are displayed on each page, and the first page is displayed
LIMIT Paging declaration
The first page is from 0 Start

LIMIT The location of

8.0 Version new features

Multi-table query （ Relational query ）

Why multi table query ： Generally speaking, it is when querying , If you need to get... In multiple tables some Field , It takes many times select operation , However, multi table query can be performed directly once .

Error due to missing connection condition

Operate correctly

You can alias a table , stay SELECT and WHERE Aliases for tables used in .
If you alias a table , Once in a SELECT and WHERE Aliases for tables used in , You must use the alias of the table , You can't use the original name, otherwise you will report an error .

If less than n-1 individual , Then there must be an error in Cartesian product

Classification of multi table query

Hard bone Internal connection and external connection

Internal connection

The operations just done are actually internal connections

External connection

Yes all The word , It must be an external connection

Above is sql92 grammar

sql99 grammar

About full external connection Mysql I won't support it FULL JOIN

99 Of 7 Ways of planting

union and union all



Recommended ON,USING The scope of use is relatively narrow

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summary

This is to follow the course of Shang Silicon Valley , The course feels very good, and I plan to continue . Let's start with a more .