mysql SQL statement, library operation

1. What is sql statement

Structured Query Language (SQL) is abbreviated as SQL. Structured Query Language is a database query and programming language used to access data and query, update and manage relational database systems;

SQL statement is a language for operating on the database.

2. The sql language is divided into 3 types according to its functions:

1. DDL statement database definition language: database, table, view, index, stored procedure, such as CREATE DROP ALTER

2. DML statement database manipulation language: insert data INSERT, delete data DELETE, update data UPDATE, query data SELECT

3. DCL statement database control language: For example, control user's access authority GRANT, REVOKE

1. Folder (library)
    增：create database db1 charset utf8;
    改：alter database db1 charset gbk;
    check:
        View library names of all libraries
        show databases;
        View information about a library alone
        show create database db1;
    删：drop database db1;

2. Documents (tables)
    First switch folders:
        use db1;
        select database(); #View the current folder 
    Add
        create table t1(id int,name char);
    change
        alter table t1 modify name char(16);
    check
        View all table names under the current library
        show tables;
        View details of t1 table
        show create table t1;
        View table structure
        desc t1;

    delete
        drop table t1;

3. A line of content of the file (record)
    increase
        insert into db1.t1 values
        ( 1, ' fixd ' ),
        ( 2, ' lius ' )
        ( 3, ' maef ' );
    change
        update db1.t1 set name='sb' where id > 1;
    check
        select id,name from db1.t1;
    delete
        delete from db1.t1 where name = "SB" ;
     

Basic Action Statements

3. Library operation

1. Create a database

CREATE DATABASE database name charset utf8;

Note: (database naming rules)

Can be composed of letters, numbers, underscores, @, #, $
case sensitive
uniqueness
Cannot use keywords such as create select
Numbers cannot be used alone
Up to 128 bits

2. Database operation

View all library names
show databases; 
view the information of a database alone
show create database db1; 
view the current database
select database();
select database
USE database name
delete database
DROP DATABASE database name;
Modify the database ( the main modification is the character encoding of the library, and the name of the library cannot be modified. )
alter database db1 charset utf8;