Question

我的SQL Server数据库中有一个名为dayorder的表，其中包含以下字段：

dayorder_cod (autoinc id),
dayorder_number (order number),
dayorder_sequence (order sequence)
dayorder_parent (parent order, can be null).

所以我可以订购100,200,998和999，其中100是998和999的母公司。

我想按如下方式对结果进行排序：100,998,999,200，即订单的子项位于其父级之下。

Answer 1

不需要加入：

如果dayorder_parent引用dayorder_number，则：

select d.*
from dayorder d
order by 
  isnull(d.dayorder_parent,d.dayorder_number)
  , d.dayorder_number

如果dayorder_parent引用dayorder_cod，则：

select d.*
from dayorder d
order by 
  isnull(d.dayorder_parent,d.dayorder_cod)
  , d.dayorder_cod

如果dayorder_sequence对订单重要

select d.*
from dayorder d
order by 
  isnull(d.dayorder_parent,d.dayorder_cod)
  , d.dayorder_sequence

工作原理：查询结果按dayorder_parent排序，但每个订单的初始行的NULL值为dayorder_parent。

使用isnull(d.dayorder_parent,d.dayorder_number)我们可以说当订单没有父订单时，请改用dayorder_number。 100名儿童与100名儿童分组，每组进一步按其个人dayorder_number排序。

注意：您可以使用coalesce()代替isnull()来获得相同的结果。我倾向于仅在需要从一组3个或更多值中获取第一个非空值时使用coalesce()，因为isnull()仅支持两个参数。

Answer 2

试试这个：

SELECT t1.*
FROM dayorder AS t1
LEFT JOIN dayorder AS t2 ON t2.parent = t1.cod
ORDER BY COALESCE(t2.parent, t1.cod), t1.cod

修改

如果sequence字段确定表格中的顺序，则可以使用：

SELECT t1.* FROM dayorder AS t1 LEFT JOIN dayorder AS t2 ON t2.parent = t1.cod ORDER BY COALESCE(t2.sequence, t1.sequence), t1.sequence

按字段排序查询与另一个字段相关

2 个答案: