Update Sql column with other column values in order with conditions

Question

I am trying to update position for my player in present in table. This table consists of name , id, points and position.

Default value of points is 0 then position will be Unranked .

If two users have same points then there positions will be same.

Demo table

id  | name | points | position
1   | a    | 0      | Unranked
2   | b    | 120    | 2
3   | c    | 130    | 3
4   | d    | 120    | 1

Required result should be

id  | name | points | position
1   | a    | 0      | Unranked
2   | b    | 120    | 2
3   | c    | 130    | 1
4   | d    | 120    | 2

Query will be like for unranked update mytable set position = 'Unranked' Where points = 0 How will i use points and position set query ?

Answer 1

This is a pain. You can get the results you want with a subquery, but that doesn't quite work in an update clause. In a select , you can do:

select t.*,
       (select 1 + count(*)
        from t t2
        where t2.points > 0 and t2.points > t.points
       ) as rank
from t;

You can now incorporate this into an update:

update t join
       (select t.*,
               (select 1 + count(*)
                from t t2
                where t2.points > 0 and t2.points > t.points
               ) as new_position
        from t;
       ) tt
       on t.id = tt.id
    set t.position = tt.new_position
    where t.points > 0;

Answer 2

There's no need to hold the computed column position in the table. The following works for all versions :

create table tab ( id int, name varchar(1), points int );
insert into tab values
(1,'a',  0),
(2,'b',120),
(3,'c',130),
(4,'d',120);
select t.id, t.name, t.points, 
       ( case when points = 0 then 'Unranked' else t.rnk end ) as position
  from
  (
    select t1.*,  
           @rnk := if(@pnt = points,@rnk,@rnk + 1) rnk,
           @pnt := points
      from tab t1 
     cross join (select @rnk := 0, @pnt := 0 ) t2
      order by points desc
   ) t
 order by t.id;

id  name  points  position
--  ----  ------  --------
1    a      0     Unranked
2    b     120       2
3    c     130       1
4    d     120       2

If you want to hold the column position in your table, then you can use the following update statement by binding through primary column id :

 update tab tt
    set position = ( select 
                     ( case when points = 0 then 'Unranked' else t.rnk end ) as position
                      from
                      (
                        select t1.*, 
                               @rnk := if(@pnt = points,@rnk,@rnk + 1) rnk,
                               @pnt := points
                          from tab t1 
                         cross join (select @rnk := 0, @pnt := 0 ) t2
                          order by points desc
                       ) t                    
                      where t.id = tt.id );

Rextester Demo

Answer 3

If your version of MySQl (MySQL 8.x) supports window function then following is possible:

SELECT name,
RANK() OVER (
    ORDER BY points DESC
) position
FROM mytable
where points != 0

Selected data can be then joined for the update like in the answer from Gordon Linoff.