SQL update

I have an MySQL database with a table "players".


One record:
playerid: 1
quality: 90
round: 1
gain: 0

Another record:
playerid: 1
quality: 92
round: 10
gain: 0

I have a couple of thousand playerid's
Each playerid has (for now) two records; one for round=1 and one for existing round (10 in the example).


I need some update sentence that goes though all my playerids where round=10 (existing round) and alter gain to last quality subtracted first quality, hence sets gain=2 in the last of the two records...

This is how I want my second record to look:
playerid: 1
quality: 92
round: 10
gain: 2   <- different

kvaadeAsked:
Who is Participating?
 
Guy Hengel [angelIII / a3]Connect With a Mentor Billing EngineerCommented:
this should do
select t.playerid, t.quality round_1_quality, c.quality round_current_quality, c.quality - t.quality as gain
  from yourtable t
  left join yourtable c
    on t.playerid = c.playerid
   and c.round = 10
 where t.playerid = 1
   and t.round = 1 

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