获取分隔字符串中某个值的第 2 次或第 3 次出现

Question

我有下表：

==========================================================
|  Name_Level_Class_Section   |   Phone Num              |
==========================================================
|  Jacky_1_B2_23              |  1122554455              |
|  Johnhy_1_B2_24             |  1122554455              |
|  Peter_2_A5_3               |  1122554455              |
==========================================================

我正在考虑将我的 SQL 语句简化如下：

select 
    *, 
    substring(Name_Level_Class_Section, 
              CHARINDEX('_',Name_Level_Class_Section,
              (CHARINDEX('_', Name_Level_Class_Section) + 1)) + 1, 
      CHARINDEX('_',Name_Level_Class_Section,
     (CHARINDEX('_',Name_Level_Class_Section,
     (CHARINDEX('_',Name_Level_Class_Section)+1))+1))-    
      CHARINDEX('_',Name_Level_Class_Section,
     (CHARINDEX('_',Name_Level_Class_Section)+1))) as CLA 
from 
    Bookings 
order by 
    CLA asc, Name_Level_Class_Section asc

这样当我执行 SQL 时，它会给我以下结果：

==========================================================
|  Name_Level_Class_Section   |  Phone Num     |  CLA    |
==========================================================
|  Jacky_1_B2_23              |  1122554455    |  B2     |
|  Johnhy_1_B2_24             |  1122554455    |  B2     |
|  Peter_2_A5_3               |  1122554455    |  A5     |
==========================================================

有什么方法可以简化我的 SQL？

Answer 1

您可以使用cross apply和 的第三个参数charindex来获取下划线的位置。

declare @T table
(
  Name_Level_Class_Section varchar(25)
)

insert into @T values
('Jacky_1_B2_23'),
('Johnhy_1_B2_24'),
('Peter_2_A5_3')

select substring(Name_Level_Class_Section, P2.Pos + 1, P3.Pos - P2.Pos - 1)
from @T
  cross apply (select (charindex('_', Name_Level_Class_Section))) as P1(Pos)
  cross apply (select (charindex('_', Name_Level_Class_Section, P1.Pos+1))) as P2(Pos)
  cross apply (select (charindex('_', Name_Level_Class_Section, P2.Pos+1))) as P3(Pos)

结果：

-------------------------
B2
B2
A5

更新：使用您的表，查询将如下所示：

select *, 
       substring(Name_Level_Class_Section, P2.Pos + 1, P3.Pos - P2.Pos - 1) as CLA
from Bookings
  cross apply (select (charindex('_', Name_Level_Class_Section))) as P1(Pos)
  cross apply (select (charindex('_', Name_Level_Class_Section, P1.Pos+1))) as P2(Pos)
  cross apply (select (charindex('_', Name_Level_Class_Section, P2.Pos+1))) as P3(Pos)
order by CLA asc,
         Name_Level_Class_Section asc

更新 2：

如果您确定您的值从不包含句点.并且它始终是一个四部分名称，您可以使用parsename。

select *, 
       parsename(replace(Name_Level_Class_Section, '_', '.'), 2) as CLA
from Bookings
order by CLA asc,
         Name_Level_Class_Section asc