MySQL-如果两个加数相同，则增加总和值

Question

Struggling a few hours on a simple MySQL update syntax . Table 's votesum column is a sum of vote1 + vote2 column. If there are several votesum values that are equal to each other ( 20 and 20 like the example below ), I need to increase the votesum by 1 for the row that has the upper vote1 value.

Table :

id|vote1|vote2|votesum
 1|10   |10   |20
 2|5    |15   |20
 3|2    |2    |4
 4|1    |1    |2

The MySQL update syntax I am looking for should check if maximum number of votesum is alone, or there are more equal votesum values. If there are two (or more) of them, then I need to increase value of votesum .

So after update table should look as follow:

id|vote1|vote2|votesum
 1|10   |10   |21
 2|5    |15   |20
 3|2    |2    |4
 4|1    |1    |2
 5|0    |2    |2

Remember that the top value of votesum are the ones that I needed to update. In the example above, id=1 and id=2 cannot be equal, but id=4 and id=5 can be equal, as I don't pay attention to those votesum values that isn't a top value.

Answer 1

I think this will do what you want:

update table t1 join table t2 on t1.votesum = t2.votesum and t1.vote1 > t2.vote2 set t1.votesum = t1.votesum + 1 order by t1.votesum limit 1

Answer 2

The following query uses variables to calculate the incremental value:

    select t.*,
           @inc := if(@votesum = votesum, @inc + 1 , 0) as inc,
           @votesum := votesum
    from t cross join
         (select @votesum := -1, @inc := 0) const
    order by votesum desc, vote1 asc;

This can be used in an update statement, using a join :

update t join
       (select t.*,
               @inc := if(@votesum = votesum, @inc + 1 , 0) as inc,
               @votesum := votesum
        from t cross join
             (select @votesum := -1, @inc := 0) const
        order by votesum desc, vote1 asc
       ) inc
       on t.id = inc.id and inc.inc > 0
    update t.votesum = t.votesum + inc.inc;