在 SQL Server 中将字符串拆分为列

Question

我在学生表中有一个名称字段，它是一个逗号分隔的字符串，格式为“LastName，FirstName，Middle Name”。在 SQL 查询中执行 select 语句时，我需要将其分解为单独的字段。我该如何实现这在 SQL 中？。有时中间初始值不可用。

SUBSTRING(Name,CHARINDEX(',',Name,1)+2,LEN(Name)) AS FirstName,
SUBSTRING(Name,1,CHARINDEX(',',Name,1)-1) AS LastName,

上面的代码在没有中间名的情况下可以正常工作。

Answer 1

这应该可以满足您的需求：

declare @tmp table (fullname varchar(100));
insert @tmp values('James, Billy, L'), ('John, Snow');

select
    fullname
    , [Last Name]
    , case
        when charindex(',', Remainder, 0) > 0
            then ltrim(substring(Remainder, 0, charindex(',', Remainder, 0)))
        else ltrim(Remainder)
    end [First Name]
    , case
        when charindex(',', Remainder, 0) = 0
            then NULL
        else ltrim(substring(Remainder, charindex(',', Remainder, 0) + 1, len(Remainder)))
    end [Middle Name]
from
(select
    fullname
    , substring(fullname, 0, charindex(',', fullname, 0))                       [Last Name]
    , substring(fullname, charindex(',', fullname, 0) + 1, len(fullname))       [Remainder]
from @tmp) result;

Answer 2

首先在字符串中找到逗号（，）的出现。然后使用CASE 表达式获取逗号的个数。如果有 2 个逗号，那么我们可以假设中间名也在那里。如果 1 则只有名字和姓氏。然后使用LEFT、RIGHT、SUBSTRING、CHARINDEX字符串函数的组合。

查询

select t.name, 
left(
    t.name, 
    charindex(',', t.name, 1) - 1
) last_name,
case t.comma_num 
when 2
then substring(
         t.name, 
         charindex(',', t.name, 1) + 1, 
         len(name) - 
         (charindex(',', t.name, 1) + 1) - charindex(',', reverse(t.name), 1) + 1
)
when 1 
then right(
         t.name, 
         charindex(',', reverse(t.name), 1) - 1
)
else null end as first_name,
case t.comma_num 
when 2 
then right(
         t.name, charindex(',', reverse(t.name), 1) - 1
) 
else null end as middle_name
from (
    select name, 
    len(name) - len(replace(name, ',', '')) comma_num
    from [your_table_name]
)t;

Find demo here

Answer 3

Use CTE and SUBSTRING AND CHARINDEX funntions 

DECLARE @Name VARCHAR(100) = 'James, Billy, L' 
--DECLARE @Name VARCHAR(100) = 'James, '', L'  

;WITH _CTE ( SplitedNames ,RemainStr) AS
(
    SELECT SUBSTRING(@Name,0,CHARINDEX(',',@Name)),
           SUBSTRING(@Name,CHARINDEX(',',@Name)+1,LEN(@Name))
    UNION ALL
    SELECT CASE WHEN CHARINDEX(',',RemainStr) = 0 THEN RemainStr ELSE       
           SUBSTRING(RemainStr,0,CHARINDEX(',',RemainStr)) END, 
           CASE WHEN CHARINDEX(',',RemainStr) = 0 THEN '' ELSE   
           SUBSTRING(RemainStr,CHARINDEX(',',RemainStr)+1,LEN(RemainStr))  
           END
    FROM _CTE 
    WHERE RemainStr <> '' 
)

SELECT SplitedNames FROM _CTE