group by and order mysql command by li'mit use and Skills

group by + polymerizable function formula:

max maximum value;

minimum min;

avg average;

sum sum;

calculated count the number of columns;

Specific examples:

select count (*) from table name; # lists the number of columns in the table

select count (user) from table name; # lists the number of columns in the table user columns

# Here to find out where you can use with

select count (id) from table where name = root; how many names there are for the statistics # id root of

# But I feel this count function used much, but behind like max, min, sum used more

Mysql below comes with a user database

select  user, count(host)  from  mysql.user;

 

 

 

select user, count (user) from group by user; #t user statistics and calculate the number of how many users

 

 

 

Like the above-mentioned sum function as long as the replacement count function on the line #, but the need for sums required for the job.

 

order by sorting the data output

 

select user, count (host) from mysql.user group by user order by host; host # number of statistics in the user table and sorted in ascending sort order by default, may join desc parameter in descending order;

 

limit parameters, and the general application scenario with order by using the number of lines from the definition of the role of access to data;

select user, count (host) from mysql.user group by user order by host limit 5; front-line # 5 to the parameters