### MySQL database DataBase

### MySQL database DataBase 
 1. persistent storage of data, in fact, is a database file system 
 2. convenience store and manage data 
 3. Use a unified way to operate the database the --sql 
 
  MySQL-uroot--proot 
  unloading 
  must clean uninstall 
  find the installation directory the my.ini configuration file 
  datadir = "c: / ProgramData / MySQL / MySQL Server 5.5 / data /" 
  after uninstalling the software 
  above the path to store the data files, but also delete a clean 
  
  view right-service --- cmd to open as administrator cmd, 
  cmd --- services.msc 
  stop --- net stop mysql database 
  start --net start mysql mysql is the name of the service, not necessarily the same 
  
  login mysql -uroot -proot 
    or mysql -uroot -p enter password 
    remotely connect to the database -HIP 
    MySQL -h127.0.0.1 -uroot--p Enter 
  exit exit 
  or quit 
  
  2.2.7.22 
  DML- additions and deletions to the data in table 
  DQL- lookup table records' select * from table; 
  1. syntax:
    select 
== aliases
        Column name field 
    from 
        table names 
    where 
        condition list 
    group by 
        grouping field 
    having 
        conditions after the packet 
    order by 
        sorting   
    limit 
        tab defines           
  2. Basic query                   
== query name and age 
    SELECT NAME, the FROM of AGE Student;      
== remove duplicate set of results 
    SELECT Student the FROM address the DISTINCT; 
== calculation math and english and fractions of 
    the SELECT NAME, math, english, math + english the FROM Student; 
- if null operation involved, results are null 
    the SELECT NAME, math, english, math + the IFNULL (Dictionary Dictionary English, 0) FROM student;
    SELECT NAME, math, english, math + IFNULL (english, 0) AS score FROM student;
        SELECT NAME, math mathematics, english English, math + IFNULL (english, 0) total score FROM student;