SQL Query: Remove multiple characters strings in a long varchar(max) column - sql

Question

I have the following string in a varchar(max) column:
PREV - FirstName: John / LAST - FirstName: Johan; PREV- LastName: Crescot / LAST - LastName: Crescott;
After every semicolon can come endless amounts PREV values and LAST value mutations depending on the amount of changes done in the source system.
I need to write a query that returns ONLY the PREV values. In case of the string above, the desired result would be:
FirstName: John; LastName: Crescot
All the slash (/) delimiters and dashes need to be removed as well, as you can see in the required result.
Could anyone help me with this? Thank you all!

Answer 1

If open to a UDF, consider the following.
Tired of extracting strings (charindindex, patindex, left, right...), I modified a parse function to accept two non-like parameters. In this case a 'PREV' and '/'
Example
Declare #YourTable table (ID int,SomeCol varchar(max))
Insert Into #YourTable values
(1,'PREV - FirstName: John / LAST - FirstName: Johan; PREV- LastName: Crescot / LAST - LastName: Crescott;')
Select A.ID
,B.NewVal
From #YourTable A
Cross Apply (
Select NewVal = Stuff((Select '; '+ltrim(rtrim(replace(RetVal,'-','')))
From [dbo].[udf-Str-Extract](A.SomeCol,'PREV','/')
For XML Path ('')),1,2,'')
) B
Returns
ID NewVal
1 FirstName: John; LastName: Crescot
The UDF if Interested
CREATE FUNCTION [dbo].[udf-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].[udf-Str-Extract] (#String,'[[',']]')
*/

Answer 2

create table #temp(val varchar(max))
Insert into #temp values('PREV - FirstName: John / LAST - FirstName: Johan; PREV - LastName: Crescot / LAST - LastName')
Select stuff(
(SELECT ';'+
Replace(stuff(Tbl.Col.value('./text()[1]','varchar(50)'),charindex('/',Tbl.Col.value('./text()[1]','varchar(50)')),len(Tbl.Col.value('./text()[1]','varchar(50)')),''),'PREV -','')as ColName
FROM
(Select cast('<a>'+ replace((SELECT val As [*] FOR XML PATH('')), ';', '</a><a>') + '</a>' as xml)as t
from #temp) tl
Cross apply
tl.t.nodes('/a') AS Tbl(Col) for xml path(''),type).value('.','NVARCHAR(MAX)'),1,2,'')
This method does not need any additional UDF.
Breaking down the above query for easy understanding:
1. Convert one row of string to multiple rows based on semicolon ';'
SELECT
Tbl.Col.value('./text()[1]','varchar(50)')
FROM
(Select cast('<a>'+ replace((SELECT val As [*] FOR XML PATH('')), ';', '</a><a>') + '</a>' as xml)as t
from #temp) tl
Cross apply
tl.t.nodes('/a') AS Tbl(Col)
2.Over the above extracted value ,use replace and stuff commands to remove unnecessary characters
SELECT
Replace(stuff(Tbl.Col.value('./text()[1]','varchar(50)'),charindex('/',Tbl.Col.value('./text()[1]','varchar(50)')),len(Tbl.Col.value('./text()[1]','varchar(50)')),''),'PREV -','')as ColName
FROM
(Select cast('<a>'+ replace((SELECT val As [*] FOR XML PATH('')), ';', '</a><a>') + '</a>' as xml)as t
from #temp) tl
Cross apply
tl.t.nodes('/a') AS Tbl(Col)
3. Use stuff and xml path to make the multiple rows back to a single row separated by semicolons as required
Select stuff(
(SELECT ';'+
Replace(stuff(Tbl.Col.value('./text()[1]','varchar(50)'),charindex('/',Tbl.Col.value('./text()[1]','varchar(50)')),len(Tbl.Col.value('./text()[1]','varchar(50)')),''),'PREV -','')as food_Name
FROM
(Select cast('<a>'+ replace((SELECT val As [*] FOR XML PATH('')), ';', '</a><a>') + '</a>' as xml)as t
from #temp) tl
Cross apply
tl.t.nodes('/a') AS Tbl(Col) for xml path(''),type).value('.','NVARCHAR(MAX)'),1,2,'')