Escape a string in SQL Server so that it is safe to use in LIKE expression

To escape special characters in a LIKE expression you prefix them with an escape character. You get to choose which escape char to use with the ESCAPE keyword. (MSDN Ref)

For example this escapes the % symbol, using \ as the escape char:

select * from table where myfield like '%15\% off%' ESCAPE '\'

If you don't know what characters will be in your string, and you don't want to treat them as wildcards, you can prefix all wildcard characters with an escape char, eg:

set @myString = replace( 
                replace( 
                replace( 
                replace( @myString
                ,    '\', '\\' )
                ,    '%', '\%' )
                ,    '_', '\_' )
                ,    '[', '\[' )

(Note that you have to escape your escape char too, and make sure that's the inner replace so you don't escape the ones added from the other replace statements). Then you can use something like this:

select * from table where myfield like '%' + @myString + '%' ESCAPE '\'

Also remember to allocate more space for your @myString variable as it will become longer with the string replacement.

Had a similar problem (using NHibernate, so the ESCAPE keyword would have been very difficult) and solved it using the bracket characters. So your sample would become

WHERE ... LIKE '%aa[%]bb%'

If you need proof:

create table test (field nvarchar(100))
go
insert test values ('abcdef%hijklm')
insert test values ('abcdefghijklm')
go
select * from test where field like 'abcdef[%]hijklm'
go