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truncate table powerrank; 
truncate table covertrank; 

insert into powerrank (ID) Select ID From UserDetails Order By power DESC; 
insert into covertrank (ID) Select ID From UserDetails Order By covert DESC; 

update UserDetails Set rank = ("select (powerrank.Rank + covertrank.Rank)/2 from
powerrank inner join covertrank on powerrank.ID = covertrank.ID 
where powerrank.ID = UserDetails.ID")