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MySQL database basic topic is coming! Hee-hee, this term I learned the fundamentals of MySQL database, and then I have sorted out some simple questions that are useful for MySQL database, I hope you can help! Say nothing, go dry! Table structure management 1. Objectives 1. Creation and deletion of MySQL database 2. Create, modify, delete ...

preface When I first saw others using Docker, I was puzzled. Why and how to use Docker? Why is Docker configuration so difficult? Why is network access blocked? And other factors hinder the author from learning Docker? In fact, the author is also very stupid. There are many points where I don't think clearly. By the way, share it. Class hour ...

Let's talk about the principle first: There are previous articles and next articles (previous articles and next articles), which must be an effect in a query set (list) obtained under the scenario of search conditions and fixed sorting rules. 1. We use rownum (a self increasing label in order) to query the result set under these two conditi ...

Things to be determined before inquiry Query several tablesLink condition of queryFields used in queryQuery criteria 1, Cross connect query The results of multi table query and cross join query will produce Cartesian product, which can not be used The result of the query is to multiply the data of the two tables select * from category,produ ...

Operation of summary table Summarize according to Master Kang's video tutorial, which is convenient for individuals to review, query and use Create and manage tables #Create database CREATE DATABASE IF NOT EXISTS XXXXXX; # CREATE DATABASE XXXXXX CHARACTER SET 'UTF8'; #Use database USE XXXXXX; #modify the database ALTER DATABASE xxxxxx CHARA ...

Query syntax # When querying all data in the table select #When querying by criteria select Field list from Table name list where Condition list group by Grouping field having Post grouping condition order by sort limit paging sql execution order from < join<where<group by <count(*)<having<select<order by <l ...

1. Index index 1. Definition Indexing is a fast, ordered data structure that helps databases efficiently retrieve data. In addition to data, the database system maintains data structures (additional storage space) that satisfy specific lookup algorithms, which point to the data in some way so that efficient lookup algorithms can be implemente ...

Relational mapping The relational mapping in the database can be one-to-one, one to many and many to many. 1, One on one When two tables have a one-to-one relationship, define a foreign key inside any model class. Create a one-to-one mapping: class A(models.Model): pass class B(models.Model): a=models.OneToOneField(A,on_delete=***) Aft ...

1, Extremely simplified deployment One click deployment with docker advantageshortcomingSimple, fast, true one click deploymentThis is a miniaturized deployment and is suitable for private use. If it needs to be used by more than one person, it is recommended to adopt the normal deployment mode 1. Install docker centos 6 installation met ...

Introduction: in the morning, I received a text message with the content of "Dear Hello, XXX". At that time, I smiled. It's a joke that programmers can Get. It shows that the program doesn't Get my name correctly from the database, and then formats the null value as null. To get back to business, the reason for this situation i ...