我可以使用 SQL 的游标从上一行检索值吗？

Question

我正在开发一个查询，我需要当前行的某个字段是“当前行的字段”+“上一行的同一字段”的结果。 (SQL Server 2008)

如何使用游标来做到这一点？

Answer 1

将上一行值分配给变量：

declare @previosvalue varchar(100) = null;
declare @currentvalue varchar(100);

declare crs cursor for select value from table;
open crs;

fetch next from crs into @currentvalue;
while @@fetch_status = 0
begin
   -- process here. On first row, @previousvalue is NULL
   -- as it should be, since there is no 'previous' of first

   select ... from sometable
   where somecondition = @currentvalue
   and othercondition = @previousvalue;

   set @previousvalue = @currentvalue;
   fetch next from crs into @currentvalue;
end

close crs;
deallocate crs;

Answer 2

这是使用 CTE 的合适解决方案吗？

WITH MyCTE AS
    (SELECT ROW_NUMBER() OVER (ORDER BY col1) AS Sequence, Col1, Col2
    FROM Table1)

SELECT c1.Sequence, c1.Col1 AS Prev_Co1,
    c2.Col1 AS Cur_Col1, c1.Col2 AS Prev_Col2, c2.Col2 AS Cur_Col2,
    COALESCE(c1.Col2, 0) + COALESCE(c2.Col2, 0) AS Sum_Col2
FROM MyCTE AS c1
LEFT OUTER JOIN MyCTE AS c2 ON c1.Sequence = c2.Sequence + 1
;

Answer 3

我确实相信 FETCH PRIOR 在 SQLServer 2008 中可用....参见
此 MS 页面