declare @a varchar(10)
set @a = 'abcd a_b'

select patindex('%[ _]%', @a)

declare @a varchar(10)
set @a = 'abcd a_b'

select patindex('%[ _]%', @a)

declare @a varchar(10)
set @a = 'abcd a_b'
select charindex('_', @a)

Far away is close at hand in the images of elsewhere.

Anon.

declare @a varchar(10)
set @a = 'abcd a_b'
select charindex('cd', @a)	             -- matches a pattern - 'cd' is found in @a 
select charindex('ce', @a)	             -- matches a pattern - 'ce' not found in @a 
select patindex('%[zce]%', @a)         -- treats each of the letters as seperate and tries to find any   
                                                    --1 of them in @a
select patindex('%[ce]%', @a)           --  same outcome as above

Far away is close at hand in the images of elsewhere.

Anon.