Introduction and advanced level of MySQL (5)

---

1、Navicat in SQL How to write it

① It is recommended to use after proficiency

② Use black window
Tools

There is a command line interface

2、 frequently-used SQL

2.1、 Query which databases are

Be careful ： A semicolon yes We SQL Finished mark , Do not belong to SQL The content of . In the future, we java I just need to write SQL that will do You don't need to write a semicolon .

2.2、 Create a new database

When we write the project You need to start with creating a database
create database Database name

2.3、 Using a database

We are now Created a database called mytest, We need to be early mytest Create a new database table in . At this time, if you need to mytest Operation in The first thing you need to To indicate which database to use
( use Database name )

here Let's operate again Is in the mytest The operation under the database .
Be careful ：

stay near After the word is us sql What went wrong , But not necessarily It could be front or back

2.4、 Check which database tables are in the database

Prove that there are no database tables in this database Empty set

2.5、 Create database tables

grammar ：
( Relational database uses tables to store data , The table is divided into rows and columns , The parentheses behind the table are the columns that customize the current table )
create table Table name (
Name data type [ constraint ] ,
Name data type [ constraint ]
Name data type [ constraint ]
Name data type [ constraint ]
Name data type [ constraint ]
…
)

Be careful ： constraint
primary key Primary key
auto_increment Auto increment
data type
int integer
varchar(20) The string type is equivalent to java Medium String 20 Represents the length Be careful Be sure to have length

2.6、 View table structure

desc Table name

2.7、 Add data ------ DML operation

Add a row
① Add a row of data to the specified column

representative Go to student Add a row of data to the table also name The column is Zhang San age yes 18 address It's Beijing.

Be careful here We didn't add id Value of class id It's worth it The reason lies in id When we create this column, we set Auto increment , When we add data Even if no value is specified It will also be added automatically .

③ If there are many columns Want to add it all At this time, you can not specify columns

④ One insert Add multiple rows of data

2.8、 The entire contents of the query table ------ DQL

2.9、 Modify the statement ------ DML

update Table name set Name = value

Be careful without where Conditional statement At this time, it means that the whole table is modified
You can also change multiple columns of data

And support operations
for example Add the age of everyone to the original basis 3 year

2.10、 Delete statements

2.11、 Delete table Delete library run