mysql 并列与非并列排名

这地方的排名分为并列排名 先看sql

方式一:

select s1.emp_no,s1.salary,count(distinct s2.salary)
from salaries as s1 ,salaries as s2
where s1.to_date='9999-01-01' 
    and s2.to_date='9999-01-01'
    and s1.salary<=s2.salary
group by s1.emp_no,s1.salary
order by s1.salary desc,s1.emp_no asc

方式二:

select s.emp_no ,s.salary,
case 
when @rowtotal = s.salary then 
   @rank 
when @rowtotal := s.salary then 
   @rank := @rank+1
when @rowtotal:=0 then
     @rank:=@rank+1
END as rank  from salaries s , (SELECT @rank := 0 ,@rowtotal := NULL) r where s.to_date = '9999-01-01'  ORDER BY s.salary desc,s.emp_no asc 

非并列排名:

select s.emp_no,s.salary ,@curRank := @curRank + 1 AS rank   
from salaries s,(SELECT @curRank := 0) t where s.to_date = '9999-01-01'  ORDER BY s.salary desc

:= 与 = 区别

= 
只有在set和update时才是和:=一样，赋值的作用，其它都是等于的作用。鉴于此，用变量实现行号时，必须用:=
:= 
不只在set和update时时赋值的作用，在select也是赋值的作用。