MySQL operation Basics

database ： Save and process data
1： species Mysql    Sql Server   DB2   Oracel
SQL sentence

Open the terminal
yum   -y   install   mysql-server   mysql         install Mysql
service   mysqld    start             start-up mysql service
mysql   -uroot                  Sign in mysql

database --- Data sheet --- data
Folder hierarchy
Server side
client
data In order to excel In the form of a table
Text data ：varchar(100)
Digital data ：int
ERROR     Error message

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Additions and deletions
1：show   databases;                    Check which databases the current server has
2：create  database  Library name ;                    Create a database
3：use   Library name ;                        choice / Enter a database
4：show   tables;                        See which tables are in the current library
5：create   table   Table name ( Name    type );                  Create a data table
      create   table   abc( full name varchar(100), Age   int, Gender varchar(100));
6：select  *  from Table name ;                        Query table data
7：desc   Table name ;                        Query table structure
8：insert   into   Table name   values( value 1, value 2);                       Add data
     insert   into   abc  values(' Zhang San ',20,' male ');
     insert   into   Table name ( Name )  values( value );                Specify columns to add data
9：drop database  Library name ;                    Delete table / library
      drop  table  Table name ;
10:delete  from Table name ;                    Delete data
     Copy the data ：create   table   Library name . The new name of the table   select  *  from  The old name of the table ;
11:update   Table name    set  Name =' value ';
     update   stu   set  full name =' Zhang San ';               Change data （ Entire column ）
     update   stu   set  full name =' Zhang San '  where  Age =30 or Gender =' male ';           Change data ( Specify data )

     Conditional expression        where  Name =' value '
     =     yes
     !=    No
     >   <    >=   <=
     and    and
     or       or
where  full name =' Zhang San '  and  Gender =' male '

select   function    
   Other functions ：
   - Aggregate functions
       Further processing of the result set ： Sum up , Averaging , Statistical quantity , Maximum , minimum value
       sum( Name )： Find the sum of all the data in the front row
       avg( Field name ):     Find the average of all the data in the front row
       count( Field name ): Find the quantity of all the data in the front row
       max( Field name )： Find the maximum value of all the data in the front row
       min( Field name )： Find the minimum value of all the data in the front row
       select   sum(sal)   from  emp;
   - Null valued function
    grammar ：
    ifnull( Name , hold null Replace with the information to be displayed )： When the field value is null when , Take the value of the second parameter
                                                                   When the field value is not null when , Use the value of the current field directly

4. How to use the function ：
   1） Individual test
     select Function name ;
     select concat(' study hard ',' Day day up ');
   2)  Nested tests
     select The name of the function ( Another function name ());
     select length(trim('  hello  '));

   character string （ written words ）：
       concat( character string 1, character string 2, character string 3)： String splicing
       length( character string )： The byte length of the output string （ Spaces also take up a character length ）
       upper( character string )： Capitalize all strings
       lower( character string )： Lowercase all strings
       substring( character string , Starting position , Intercept length )： Intercepts a string at a specified location
       trim( character string )： Remove the spaces on both sides of the string
       ltrim( character string )： Remove the space to the left of the string
       rtrim( character string )： Remove the space to the right of the string
       replace( character string , Replaced string , String replaced with ): String substitution
       strcmp( character string 1, character string 2): Compare the size of two strings （ Compare by text encoding ）
     chinese > english > Numbers > Symbol

   The number ：
       ceil( decimal ): Rounding up
       floor( decimal ): Rounding down
       mod( The number 1, The number 2): For the value 1 And numbers 2 Carry out the redundancy operation
select   mod(3,2)
       rand(): Generate 0-1 Random number between
       round( decimal , Keep a few decimal places ): The value is rounded to the specified decimal places

   Time ：
       now(): Get the current time, month, day, hour, minute and second
       curdate(): Get the date in the current time
       curtime(): Get the hours, minutes and seconds in the current time
       year(now()): Get the current year
       month( Specify time ): Get the current month
       day( Specify time ): Get current day
       hour( Specify time ): Get the current time
       minute( Specify time ): Get the current minute
       second( Specify time ): Get the current second
       week( Specify time ): Get the week ordinal of the current year
       weekday( Specify time ): Get the day of the week

Backup of data table
   It is a combination of creating tables and querying tables
   grammar ：
   create table The new name of the table as select * from Original table name ;
   Copy emp surface , The new table is named emp_copy
   Copy dept surface , The new table is named dept_copy
   see mydb All tables in

1. Group query
   grammar ：
   group by Grouped fields   having Filter conditions
   group  by  deptno,sex
   The rules ：
   1） There are several lines of fields with the same rule that can be grouped
   2） After grouping the fields of the same rule, the result of single row and single column will be formed
   3）having Filter conditions can be added selectively according to the situation
   4)  Multi field grouping group by Field 1, Field 2
2.SQL The execution order of the statement key ：
   from -----> where----->gorup by---->having ----->select ----->order by ---->limit

Data table field modification
describe   Table name ;
1： Add column
alter  table  Table name   add  column  Name   type ;
Specify the location to add columns
alter  table  Table name   add  column  Name   type   after  Name ;
2： Delete column
alter   table   Table name    drop  column  Name ;
3： rename table
alter   table  Table name   rename  to   The new name of the table ;
4： Modify the column
alter  table   Table name    change  column  Name    New column names    New data types ;

mysql  User management and permission settings
1： stay root Create a new ordinary user under user
create  user   'zs'@'localhost'   identified   by  '1234';
2： View user permissions
show  grants  for  'zs'@'localhost';
grant   usage   on  *.*   to   'zs'@'localhost'
3： Grant user rights
grant  create  on  a.*  to  'zs'@'localhost';     Grant users the right to create libraries a jurisdiction
4： Reclaim user rights
revoke  create  on  a.*  from  'zs'@'localhost';     Recycle user created Libraries a jurisdiction
5： Operation permissions on Columns
grant  alter  on  a.*  to  'zs'@'localhost';
6： Grant users permission to create new users
grant   create  user  on  *.*  to 'zs'@'localhost';
7： Refresh permission table
flush  privileges;
8： Grant users ' Give yourself permission to another user ' Authority
grant  create   on  a.*   to   'B'@'localhost'  with  grant  option;    A    
grant  create  on  a.*  to 'C'@'localhost' identified  by  '1234';    B    A    B    C