Question

假设我有下表：

AAAAAA
AAAAAB
CCCCCC

我如何制作一个让我知道AAAAA和AAAAB相似的查询（因为它们共享五个字符）？理想情况下，我想把它写成一个查询，检查两个字段是否在字符串中的任何位置共享五个字符，但这似乎超出了SQL的范围，我应该写入C＃应用程序？

理想情况下，查询会添加另一列显示：Similar to 'AAAAA', 'AAAAB'

Answer 1

我建议你不要试图通过引入多值属性来违反1NF。

注意到SUBSTRING非常便携：

WITH T 
     AS
     (
      SELECT * 
        FROM (
              VALUES ('AAAAAA'), 
                     ('AAAAAB'), 
                     ('CCCCCC')
             ) AS T (data_col)
     )
SELECT T1.data_col, 
       T2.data_col AS data_col_similar_to
  FROM T AS T1, T AS T2
 WHERE T1.data_col < T2.data_col
       AND SUBSTRING(T1.data_col, 1, 5) 
              = SUBSTRING(T2.data_col, 1, 5);

Alternativvely：

T1.data_col LIKE SUBSTRING(T2.data_col, 1, 5) + '%';

Answer 2

这将找到所有匹配项，也就是在单词中间的那些匹配项，它在大桌面上表现不佳

declare @t table(a varchar(20))

insert @t select 'AAAAAA'
insert @t select 'AAAAAB'
insert @t select 'CCCCCC'
insert @t select 'ABCCCCC'
insert @t select 'DDD'

declare @compare smallint = 5

;with cte as
(
select a, left(a, @compare) suba, 1 h
from @t
union all
select a, substring(a, h + 1, @compare), h+1
from cte where cte.h + @compare <= len(a)
)
select t.a, cte.a match from @t t 
-- if you don't want the null matches, remove the 'left' from this join 
left join cte on charindex(suba, t.a) > 0 and t.a <> cte.a  
group by t.a, cte.a

结果：

a                    match
-------------------- ------
AAAAAA               AAAAAB
AAAAAB               AAAAAA
ABCCCCC              CCCCCC
CCCCCC               ABCCCCC

Answer 3

您可以使用left来比较前五个字符，并且可以使用for xml path将类似的字符串连接到一列。

declare @T table
(
  ID int identity primary key,
  Col varchar(10)
)

insert into @T values
('AAAAAA'),
('AAAAAB'),
('AAAAAC'),
('CCCCCC')

select Col,
       stuff((select ','+T2.Col
              from @T as T2
              where left(T1.Col, 5) = left(T2.Col, 5) and
                    T1.ID <> T2.ID
              for xml path(''), type).value('.',  'varchar(max)'), 1, 1, '') as Similar
from @T as T1

结果：

Col        Similar
---------- -------------------------
AAAAAA     AAAAAB,AAAAAC
AAAAAB     AAAAAA,AAAAAC
AAAAAC     AAAAAA,AAAAAB
CCCCCC     NULL

如何检查一个字段的前五个字符是否与另一个字段匹配？

3 个答案: