Làm thế nào để có được Số dư chạy mới từ Số dư hiện có?

Một Case statement có thể xử lý tình trạng của bạn.

SELECT id ID, token TK, actual_pay PAY,
       IF(@rtp IS NULL, @rtp:=token, @rtp:example@sqldat.com+actual_pay) RTP,
       IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com) BAL,

       (case IF(@rtp IS NULL, @rtp:=token, @rtp:example@sqldat.com+actual_pay)
         when IF(@rtp IS NULL, @rtp:=token, @rtp:example@sqldat.com+actual_pay) <= 
              (select token from token_table where id = a.id+1)
         then 1
        else 0
       end case) stat,

      (case IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com)
        when IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com) <= 
             (select token from token_table where id = a.id+1)
        then 0
       else 
        IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com) - 
        (select token from token_table where id = a.id+1)
      end case) nbal,

      (case IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com)
        when IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com) <= 
             (select token from token_table where id = a.id+1)           
        then
            (select token from token_table where id = a.id+1)  -
            IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com)
       else 
        IF(@bal IS NULL, @bal:=actual_pay-token, @bal:example@sqldat.com) - 
        (select token from token_table where id = a.id+1)
      end case) ntk

FROM token_table a
JOIN (SELECT @rtp:=NULL, @bal:=NULL) b;