SQL Server 2008 R2 : Update table using pattern

Question

我有下表，其中包含一些记录:

表:Test_One

create table Test_One
(
  Cola varchar(50)
);

插入记录:

Insert into Test_One values('1_123456');
Insert into Test_One values('123456898_121');
Insert into Test_One values('12345633_789');
Insert into Test_One values('986_12345622');
Insert into Test_One values('3457_123456221');
Insert into Test_One values('2_123456456');
Insert into Test_One values('1234567878_5674');
Insert into Test_One values('23_1234560976');
Insert into Test_One values('6_12345634234');
...
...
Millions

现在我想更新Cola列。我想从开头删除字符串部分 从结束。以 _ 结尾的起始字符串，如 1_,2_,23_,6_,3457_,986_ 想要删除并 以 _ 开头的结束字符串(如 _121,_789,_5674)不需要删除。

结果应该是:

Cola
-----------
123456
123456898
12345633
12345622
123456221
123456456
1234567878
1234560976
12345634234
...
...

Answer 1

使用CHARINDEX和SUBSTRING:

SELECT
    *,
    CASE
        WHEN LEN(SUBSTRING(Cola, CHARINDEX('_', Cola) + 1, LEN(Cola) - CHARINDEX('_', Cola))) >=
                LEN(SUBSTRING(Cola, 0, CHARINDEX('_', Cola)))
            THEN SUBSTRING(Cola, CHARINDEX('_', Cola) + 1, LEN(Cola) - CHARINDEX('_', Cola))
        ELSE
            SUBSTRING(Cola, 0, CHARINDEX('_', Cola))
    END AS UpdatedCola  
FROM Test_One