DQL basic operation

Alias

select * from  indicate  as  Alias 
// It's OK not to as

duplicate removal

select distinct  Field name （ Can be all ） from  Table name ; 

The query result is an expression

select price+10 from  Table name ;

wildcard

%a  The bad ending is a Of 
%a%  Query contains a Of 
a%  The query starts with a Of 

use least For the minimum

select least();
 Yes null It will not be more direct null

Sort query order by

select  Field name 
from  Table name 
order by  Field one [desc]
// Default ascending order desc Descending ,order by  In the last 

Aggregate query

count The sum of the trips （ No matter null）

sum The sum of the columns

max Maximum

min minimum value

avg Average

Group query

select  Field name , Aggregate functions  from  Table name  group by  Grouping field  having  Grouping conditions 

Add one at the end of paging query limit m,n; Important chapter m+1 Start checking n The bar is usually placed at the end of the statement

sql Execution order of

from-->where-->group by-->count()-->having--> perform -->select-->order by-->limit