Select string between "\" and "." in SQL Server - sql-server

Question

I have the following table column named file and it contains directories.
Sample data is:
C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML
C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML
Note that I only want to get 6860_f11.xlxb for #1 and 1191_f12.xlxb for #2.
For #1, the directory only contains 1 folder filedata but for #2 it contains 2 folders cloud\files
Below is my code:
select
(SUBSTRING((file), 0, CHARINDEX ('.xlxb', (file)) + 4)) as xlsb_file
from
[Projects].[dbo].[ProjFiles]
Is there any way I could get the string after the folder and until the underscore after .xlxb?

Answer 1

No CLR needed. No Regex required. The easiest and best performing way to solve this using NGrams8K. It's 2AM where I live so I'll make this quick.
Note this query:
DECLARE #string VARCHAR(150) = 'C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML';
SELECT RetPos = f.p, RetVal = e.s
FROM (SELECT MAX(position)+1 FROM samd.NGrams8k(#string,1) WHERE token = '\') AS f(p)
CROSS APPLY (VALUES(SUBSTRING(#string,f.p,CHARINDEX('.',#string,f.p)-f.p+5))) AS e(s);
Results:
RetPos RetVal
------ ---------------
16 1191_f12.xlxb
Now Against a table:
CREATE TABLE #yourtable ([file] VARCHAR(150));
INSERT INTO #yourtable
VALUES ('C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML'),
('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML');
SELECT *
FROM #yourtable AS t
CROSS APPLY
(
SELECT newstring = e.s
FROM (SELECT MAX(position) FROM samd.NGrams8k(t.[file],1) WHERE token = '\') AS f(p)
CROSS
APPLY (VALUES(SUBSTRING(t.[file],f.p+1,CHARINDEX('.',t.[file],f.p+1)-f.p+4))) AS e(s)
) AS itvf_str_extract;
It's really that easy. The performance will beats the pants of any CLR/Regex Based solution too - so there's that.
On a side note: John Cappelletti's solution is excellent (as per usual). Under the hood it's very similar to my NGrams solution but not exactly; compare these two queries:
DECLARE #string VARCHAR(150) = 'C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML';
DECLARE #Delimiter1 varchar(100) = '\', #Delimiter2 varchar(100) = '.';
-- Alan B
SELECT
RetSeq = 1,
RetPos = f.p,
RetVal = e.s
FROM (SELECT MAX(position)+1 FROM samd.NGrams8k(#string,1) WHERE token = '\') AS f(p)
CROSS
APPLY (VALUES(SUBSTRING(#string,f.p,CHARINDEX('.',#string,f.p)-f.p+5))) AS e(s);
-- John C
with cte1(N) As (Select 1 From (Values(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) N(N)),
cte2(N) As (Select Top (IsNull(DataLength(#String),0)) Row_Number() over (Order By (Select NULL)) From (Select N=1 From cte1 N1,cte1 N2,cte1 N3,cte1 N4,cte1 N5,cte1 N6) A ),
cte3(N) As (Select 1 Union All Select t.N+DataLength(#Delimiter1) From cte2 t Where Substring(#String,t.N,DataLength(#Delimiter1)) = #Delimiter1),
cte4(N,L) As (Select S.N,IsNull(NullIf(CharIndex(#Delimiter1,#String,s.N),0)-S.N,8000) From cte3 S)
Select RetSeq = Row_Number() over (Order By N)
,RetPos = N
,RetVal = left(RetVal,charindex(#Delimiter2,RetVal)-1)
From (
Select *,RetVal = Substring(#String, N, L)
From cte4
) A
Where charindex(#Delimiter2,RetVal)>1;
Now the execution plans:

Answer 2

There are several ways to do it. This is one method
select substring(reverse(substring(reverse('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML'),1,charindex('\',reverse('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML'))-1)),1,13)
And if your filename is not always the same, you could do the same logic with _
This one will work with underscore - given that there is no other underscore than xlxb_
select
reverse(substring(reverse(reverse(substring(reverse('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML'),1,charindex('\',reverse('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML'))-1))),charindex('_',reverse('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML'))+1,len('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML')))

Answer 3

For such tasks it will be better to implement SQL CLR function. Here is example of how to create such. Having regex support, you can do things like the following:
DECLARE #DataSource TABLE
(
[value] VARCHAR(256)
);
INSERT INTO #DataSource ([value])
VALUES ('C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML')
,('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML');
SELECT *
FROM #DataSource DS
CROSS APPLY [dbo].[fn_Utils_RegexMatches] ([value], '[^\\]+\.xlxb');
Of course, you can create more complicate patterns to match using regular expressions.

Answer 4

If open to a Table Valued Function, consider the following.
Tired of extracting strings (left,right,charindex,patindex,etc.), I modified a parse function to accept two non-like delimiters. In this case '\' and '.xlxb'
Also being a TVF, it is easy to incorporate into a CROSS APPLY.
Example
Declare #YourTable table ([file] varchar(150))
Insert Into #YourTable values
('C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML')
,('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML')
Select A.*
,B.*
From #YourTable A
Cross Apply [dbo].[tvf-Str-Extract](A.[File],'\','.xlxb') B
Returns
file RetSeq RetPos RetVal
C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML 1 13 6860_f11
C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML 1 16 1191_f12
The TVF if Interested
CREATE FUNCTION [dbo].[tvf-Str-Extract] (#String varchar(max),#Delimiter1 varchar(100),#Delimiter2 varchar(100))
Returns Table
As
Return (
with cte1(N) As (Select 1 From (Values(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) N(N)),
cte2(N) As (Select Top (IsNull(DataLength(#String),0)) Row_Number() over (Order By (Select NULL)) From (Select N=1 From cte1 N1,cte1 N2,cte1 N3,cte1 N4,cte1 N5,cte1 N6) A ),
cte3(N) As (Select 1 Union All Select t.N+DataLength(#Delimiter1) From cte2 t Where Substring(#String,t.N,DataLength(#Delimiter1)) = #Delimiter1),
cte4(N,L) As (Select S.N,IsNull(NullIf(CharIndex(#Delimiter1,#String,s.N),0)-S.N,8000) From cte3 S)
Select RetSeq = Row_Number() over (Order By N)
,RetPos = N
,RetVal = left(RetVal,charindex(#Delimiter2,RetVal)-1)
From (
Select *,RetVal = Substring(#String, N, L)
From cte4
) A
Where charindex(#Delimiter2,RetVal)>1
)
/*
Max Length of String 1MM characters
Declare #String varchar(max) = 'Dear [[FirstName]] [[LastName]], ...'
Select * From [dbo].[tvf-Str-Extract] (#String,'[[',']]')
*/

Answer 5

For SQL Server, starting with 2016, you may use STRING_SPLIT():
CREATE TABLE #FileTable (
FullName varchar(150)
)
INSERT INTO #FileTable (FullName)
VALUES
('C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML'),
('C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML')
SELECT
f.FullName,
SUBSTRING(s.[value], 1, CHARINDEX('.xlxb', s.[value]) + LEN('xlxb')) AS FileName
FROM #FileTable f
CROSS APPLY STRING_SPLIT(f.FullName, '\') s
WHERE s.[value] LIKE '%.xlxb%'
Output:
FullName FileName
C:\filedata\6860_f11.xlxb_3.30 test - 0.3 ML 6860_f11.xlxb
C:\cloud\files\1191_f12.xlxb_12.16 test - 0.3 ML 1191_f12.xlxb