为什么有必要在数据库中显式指定外键和引用？(Why is it necessary to explicitly specify foreign keys and references in databases?)

 您将需要根据分割数据. 。 您可以使用递归CTE分割数据并返回深度： 
 
;with cte (id, DescriptionItem, Description, depth) as
(
  select id,
    cast(left(Description, charindex('.',Description+'.')-1) as varchar(50)) DescriptionItem,
         stuff(Description, 1, charindex('.',Description+'.'), '') Description,
    1 as depth
  from MyTable
  union all
  select id,
    cast(left(Description, charindex('.',Description+'.')-1) as varchar(50)) DescriptionItem,
    stuff(Description, 1, charindex('.',Description+'.'), '') Description,
    depth+1
  from cte
  where Description > ''
) 
select id, DescriptionItem, depth
from cte
order by id, depth;
 
 请参阅SQL Fiddle with Demo 
 
 或者您可以使用拆分数据的UDF函数： 
 
create FUNCTION [dbo].[Split](@String varchar(MAX), @Delimiter char(1))       
returns @temptable TABLE (items varchar(MAX), depth int)       
as       
begin      
    declare @idx int       
    declare @slice varchar(8000) 
    declare @depth int = 1

    select @idx = 1       
        if len(@String)<1 or @String is null  return       

    while @idx!= 0       
    begin       
        set @idx = charindex(@Delimiter,@String)       
        if @idx!=0       
            set @slice = left(@String,@idx - 1)       
        else       
            set @slice = @String       

        if(len(@slice)>0)  
            insert into @temptable(Items, depth) values(@slice, @depth)       

        set @String = right(@String,len(@String) - @idx) 
        set @depth = @depth +1
        if len(@String) = 0 break       
    end   
return 
end;
 
 然后当你调用该函数时，你将使用类似于此的CROSS APPLY ： 
 
select t.id, c.items description,
  c.depth
from mytable t
cross apply dbo.split(t.description, '.') c
order by t.id, c.depth;
 
 请参阅SQL Fiddle with Demo 

You will want to split the data based on the .. You can use a recursive CTE to split the data and return the depth:
 
;with cte (id, DescriptionItem, Description, depth) as
(
  select id,
    cast(left(Description, charindex('.',Description+'.')-1) as varchar(50)) DescriptionItem,
         stuff(Description, 1, charindex('.',Description+'.'), '') Description,
    1 as depth
  from MyTable
  union all
  select id,
    cast(left(Description, charindex('.',Description+'.')-1) as varchar(50)) DescriptionItem,
    stuff(Description, 1, charindex('.',Description+'.'), '') Description,
    depth+1
  from cte
  where Description > ''
) 
select id, DescriptionItem, depth
from cte
order by id, depth;
 
See SQL Fiddle with Demo
 
Or you can use a UDF function that splits the data:
 
create FUNCTION [dbo].[Split](@String varchar(MAX), @Delimiter char(1))       
returns @temptable TABLE (items varchar(MAX), depth int)       
as       
begin      
    declare @idx int       
    declare @slice varchar(8000) 
    declare @depth int = 1

    select @idx = 1       
        if len(@String)<1 or @String is null  return       

    while @idx!= 0       
    begin       
        set @idx = charindex(@Delimiter,@String)       
        if @idx!=0       
            set @slice = left(@String,@idx - 1)       
        else       
            set @slice = @String       

        if(len(@slice)>0)  
            insert into @temptable(Items, depth) values(@slice, @depth)       

        set @String = right(@String,len(@String) - @idx) 
        set @depth = @depth +1
        if len(@String) = 0 break       
    end   
return 
end;
 
Then when you call the function, you will use CROSS APPLY similar to this:
 
select t.id, c.items description,
  c.depth
from mytable t
cross apply dbo.split(t.description, '.') c
order by t.id, c.depth;
 
See SQL Fiddle with Demo