sql-server - 如何在SQL Server中将一列拆分为两列

Question

我有关于 SQL Server 的小问题，请告诉我如何解决这个问题

表:emp

   id    name
  ---------------
   1    abc_rao
   2    nani
   3    hari_babu
   4    kalibabu
   5    ab_tan

根据该表，我想要如下输出

   id   firstname   lastname
   1      abc       rao
   2      nani      nothing
   3      hari      babu
   4      kalibabu  nothing
   5      ab        tan

我尝试过这样的:

select 
    SUBSTRING(name, 1, CHARINDEX('_', name) - 1) as firstname , 
    SUBSTRING(name, CHARINDEX('_', name) + 1, LEN(name)) as lastname 
from emp

但我没有得到完全预期的结果。

相反，我收到错误:

Msg 537, Level 16, State 2, Line 3
Invalid length parameter passed to the LEFT or SUBSTRING function.

请告诉我如何解决这个问题

在 SQL Server 中使用查询时出现问题

Answer 1

试试这个:

select 
    case when CHARINDEX('_',name)>0 
         then SUBSTRING(name,1,CHARINDEX('_',name)-1) 
         else name end firstname, 
    CASE WHEN CHARINDEX('_',name)>0 
         THEN SUBSTRING(name,CHARINDEX('_',name)+1,len(name))  
         ELSE NULL END as lastname
from emp

您可以使用CASE命令来控制姓氏是否可用。

SQL Fiddle

MS SQL Server 2008 架构设置:

查询 1:

declare @t table (id int, name  varchar(50))

insert into @t (id,name) values( 1    ,'abc_rao')
insert into @t (id,name) values( 2    ,'nani')
insert into @t (id,name) values( 3    ,'hari_babu')
insert into @t (id,name) values( 4    ,'kalibabu')
insert into @t (id,name) values( 5    ,'ab_tan')

select 
    case when CHARINDEX('_',name)>0 
         then SUBSTRING(name,1,CHARINDEX('_',name)-1) 
         else name end firstname, 
    CASE WHEN CHARINDEX('_',name)>0 
         THEN SUBSTRING(name,CHARINDEX('_',name)+1,len(name))  
         ELSE NULL END as lastname
from @t

<强> Results :

| FIRSTNAME | LASTNAME |
|-----------|----------|
|       abc |      rao |
|      nani |   (null) |
|      hari |     babu |
|  kalibabu |   (null) |
|        ab |      tan |

更新:添加了 sqlfiddle