求一SELECT 计算,该如何处理

create table t(ta int ,tb char(1),tc int)
insert into t 
select 1,'a',100 union  
select 1,'b',300 union
select 1,'c',700 union 
select 2,'a',50 union
select 2,'b',80 union
select 3,'a',300 union  
select 3,'b',70  

create  Function Find(@ta int,@m int) 
returns  @r table(ta int ,tb char(1),tc int,tx int,ty int)
as 
begin 
 DECLARE TCURSOR CURSOR local FOR 
         select ta,tb,tc from t where ta=@ta;
 declare @v_ta int ,@v_tb char(1),@v_tc int;
 OPEN TCURSOR; 
 FETCH NEXT FROM TCURSOR INTO @v_ta,@v_tb,@v_tc;   
 WHILE @@FETCH_STATUS=0
    BEGIN          
          if(@m>=@v_tc)
              begin
              insert @r select @v_ta,@v_tb,@v_tc,@v_tc,0;
              set @m=@m-@v_tc;
              end
          else
              begin
                 insert @r select @v_ta,@v_tb,@v_tc,@m,@v_tc-@m;               
              end
          FETCH NEXT FROM TCURSOR INTO @v_ta,@v_tb,@v_tc;   
    END
 CLOSE TCURSOR; 
 DEALLOCATE TCURSOR;
return ;
end 


select * from Find(1,800)
union
select * from Find(2,100)
union
select * from Find(3,100)


1    a    100    100    0
1    b    300    300    0
1    c    700    400    300
2    a    50    50    0
2    b    80    50    30
3    a    300    100    200
3    b    70    70    0