SQL circularly processes the addition and subtraction of the current row data and the previous row data

Time:2021-9-13

In the following example, it is relatively simple to use the cursor to cycle the data in the table #temptable, and then add argument1 in the current row and the previous row and store it in argument2 in the current row.


--drop table #temptable
create table #temptable
(
  argument1 int,
  argument2 int,
  argument3 datetime
)

declare @rowcount int,@argument1 int,@argument2 nvarchar(50),@argument3 datetime
set @rowcount=1
set @argument1=1
set @argument2=0
set @argument3=GETDATE()

while(@rowcount<100)
begin
  insert into #temptable(argument1,argument2,argument3)
        values(@argument1,@argument2,@argument3)
  
  set @[email protected] + datepart(day,@argument3)
  set @[email protected]  
  set @rowcount = @rowcount + 1
end

--select * from #temptable

declare @lastargument2 int
set @lastargument2=0
set @argument2=0
declare _cursor cursor for(select argument1 from #temptable)
open _cursor;
fetch next from _cursor into @argument2 
while @@fetch_status = 0
begin      
  update #temptable
  set [email protected][email protected]
  where current of _cursor
  
  set @[email protected]  
  fetch next from _cursor into @argument2 
end
close _cursor
deallocate _cursor

--select * from #temptable

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First sentence fetch next from_ Why can’t the sentence “cursor into @ argument2” be placed in the first line of the while loop and delete the second line? I remember I made a mistake here, ha ha.