相同值序号一样，select中的变量是从左到右赋值生效的。

set @newrow:=0;

set @val = -0.01;

select id,(case when ifnull(@val,-1.1) <> ifnull(AAA_yfjfbz,-1.1) then @newrow:=@newrow+1 else @newrow end) as newid,(p_pcount - @newrow + 1) as star,(@val:=AAA_yfjfbz) as dbval from AAA_element where area_clstype = p_clstype order by AAA_yfjfbz desc;