Total / statistics function of MySQL

total / Statistical function

count function

select count(*) from student;

select count(*) from student where math > 90;

• count(*) and count（ Column ） The difference between
  • count（*） Return the number of rows of records that meet the conditions
  • count（ Column ） Count the number of columns that meet the conditions , But it will be excluded as null

sum function

• sum Functions only work with numbers , Otherwise, an error will be reported
• For multi column summation , It can't be less .

--  Count the total score of mathematics in a class 
select sum(math) from student;
--  Count the total score of each subject in a class 
select sum(english),sum(math),sum(chinese) from student;
--  Count the total scores of three subjects in a class 
select sum(english+math+chinese) from student;
--  The average score of a Chinese class is one 
select sum(chinese) / count(*) from student;

avg function

--  Average score of Statistical Mathematics 
select avg(math) from student;
--  Average score of statistical total score 
select avg(math + english + chinese) from student;

max/min function

--  Ask for the highest and lowest score of the class 
select max(math + english + chinese) , min(math + chinese + english) from student;
--  Seek the highest and lowest scores in class mathematics 
select max(math),min(math) from student;