sql Return string between two characters - sql

Question

I want to know a flexible way to extract the string between two '-'. The issue is that '-' may or may not exist in the source string. I have the following code which works fine when '-' exists twice in the source string, marking the start and end of the extracted string. But it throws an error "Invalid length parameter passed to the LEFT or SUBSTRING function" when there is only one '-' or none at all or if the string is blank. Can someone please help? Thanks
declare #string varchar(100) = 'BLAH90-ExtractThis-WOW'
SELECT SUBSTRING(#string,CHARINDEX('-',#string)+1, CHARINDEX('-',#string,CHARINDEX('-',#string)+1) -CHARINDEX('-',#string)-1) as My_String
Desired Output: ExtractThis
If there is one dash only e.g. 'BLAH90-ExtractThisWOW' then the output should be everything after the first dash i.e. ExtractThisWOW. If there are no dashes then the string will have a blank space instead e.g. 'BLAH90 ExtractThisWOW' and should return everything after the blank space i.e. ExtractThisWOW.

Answer 1

You can try something like this.
When there is no dash, it starts at the space if there is one or take the whole string if not.
Then I look if there is only one dash or 2
declare #string varchar(100) = 'BLAH90-ExtractThis-WOW'
declare #dash_pos integer = CHARINDEX('-',#string)
SELECT CASE
WHEN #dash_pos = 0 THEN
RIGHT(#string,LEN(#string)-CHARINDEX(' ',#string))
ELSE (
CASE
WHEN #dash_pos = LEN(#string)-CHARINDEX('-',REVERSE(#string))+1
THEN RIGHT(#string,LEN(#string)-#dash_pos)
ELSE SUBSTRING(#string,#dash_pos+1, CHARINDEX('-',#string,#dash_pos+1) -
#dash_pos -1)
END
)
END as My_String

Answer 2

Try this. If there are two dashes, it'll take what is inside. If there is only one or none, it'll keep the original string.
declare #string varchar(100) = 'BLAH-90ExtractThisWOW'
declare #dash_index1 int = case when #string like '%-%' then CHARINDEX('-', #string) else -1 end
declare #dash_index2 int = case when #string like '%-%'then len(#string) - CHARINDEX('-', reverse(#string)) + 1 else -1 end
SELECT case
when #dash_index1 <> #dash_index2 then SUBSTRING(#string,CHARINDEX('-',#string)+1, CHARINDEX('-',#string,CHARINDEX('-',#string)+1) -CHARINDEX('-',#string)-1)
else #string end
as My_String

Answer 3

Take your existing code:
declare #string varchar(100) = 'BLAH90-ExtractThis-WOW'
SELECT SUBSTRING(#string,CHARINDEX('-',#string)+1, CHARINDEX('-',#string,CHARINDEX('-',#string)+1) -CHARINDEX('-',#string)-1) as My_String
insert one line, like so:
declare #string varchar(100) = 'BLAH90-ExtractThis-WOW'
SET #string = #string + '--'
SELECT SUBSTRING(#string,CHARINDEX('-',#string)+1, CHARINDEX('-',#string,CHARINDEX('-',#string)+1) -CHARINDEX('-',#string)-1) as My_String
and you're done. (If NULL, you will get NULL returned. Also, this will return all data based on the FIRST dash found in the string, regardless of however many dashes are in the string.)