Like vs. “=” for matching strings using SQL Server

Question

Whenever I write a stored procedure for selecting data based on string variable (varchar, nvarchar, char) I would have something like:

procedure dbo.p_get_user_by_username(
    @username      nvarchar(256)
as
begin
    select
        u.username
        ,u.email
        --,etc
    from
        sampleUserTable u
    where
        u.username = @username
end

So in other words to match the record I would have

u.username = @username

But sometimes I come across code that would use LIKE in place of =

u.username like(@username)

When would you use it? Shouldn't that be used only when you need some wildcard matching?

EDIT

Thanks for the answers.

I think that I need to clarify that what I was really trying to ask was: if there could be a situation when it was preferred to use like in place of "=" for exact string matching. From the answers I could say that there would not be. From my own experience even in situations when I need to ignore e.g case, and leading and ending spaces i would use ltrim, rtrim, lower on both strings and then "=". Thanks again for your input.

Answer 1

You are correct. There is no benefit in using LIKE unless you are doing wild card matching. In addition, using it without wildcard could lead to the use of an inefficient queryplan.

Answer 2

Sunny almost got it right :)

Run the following in QA in a default install of SQL2005

select * from sysobjects where name = 'sysbinobjs   '
-- returns 1 row
select * from sysobjects where name like 'sysbinobjs   '
-- returns 0 rows

So, LIKE does not match on trailing spaces, on the query plan side both perform almost equally, but the '=' join performs a tiny bit better.

An additional thing you MUST keep in mind when using LIKE is to escape your string properly.

declare @s varchar(40) 
set @s = 'escaped[_]_%'

select 1 where 'escaped[_]_%'  like @s 
--Return nothing = BAD 

set @s = '_e_s_c_a_p_e_d_[___]___%' 

select 1 where 'escaped[_]_%'  like @s escape '_'
--Returns 1 = GOOD

In general people do not use LIKE for exact matching, because the escaping issues cause all sorts of complications and subtle bugs, people forget to escape and there is a world of pain.

But ... if you want a real exact match that is efficient, LIKE can solve the problem.

Say, you want to match username to "sam" and do not want to get "Sam" or "Sam " and unfortunately the collation of the column is case insensitive.

Something like the following (with the escaping added) is the way to go.

select * from sysobjects
WHERE name = 'sysbinobjs' and name COLLATE Latin1_General_BIN LIKE 'sysbinobjs'

The reason you do a double match is to avoid a table scan.

However ....

I think the varbinary casting trick is less prone to bugs and easier to remember.

Answer 3

If no wildcards are used, then the difference is, that "=" makes an exact match, but LIKE will match a string with trailing spaces (from SSBO):

When you perform string comparisons with LIKE, all characters in the pattern string are significant, including leading or trailing spaces. If a comparison in a query is to return all rows with a string LIKE 'abc ' (abc followed by a single space), a row in which the value of that column is abc (abc without a space) is not returned. However, trailing blanks, in the expression to which the pattern is matched, are ignored. If a comparison in a query is to return all rows with the string LIKE 'abc' (abc without a space), all rows that start with abc and have zero or more trailing blanks are returned.

Answer 4

With the LIKE keyword you can match the field u.username against a specified pattern instead of a fixed "string".

Answer 5

If you're seeing this in other people's code maybe they intended to allow a person to pass in a string that included a pattern or wildcards.

Answer 6

Yes - you are right - it should only be used for wildcard matching. It should be used sparingly especially on very large tables on non-indexed fields as it can slow your queries WAY WAY down.

Answer 7

I ran into the same problem. It took about a minute and a half to run similar query with =. When I changed = to like the query was much faster.

• Try creating an index for the column you are comparing with. This sped up the query significantly.
• Try running sp_updatestats. In my case this made the query run in about 6 seconds using = with out the index and almost instantly with the index.

Answer 8

LIKE is for wildcard matching, where as = (equals) is for an exact matches.

I also think it used for fields that have been catalogued by FULL TEXT CATALOGUES for hard core string comparisons.

Answer 9

Yes, as far as I know, using like without any wildcards is the same as using the = operator. are you sure the input parameter doesn't have wildcards in it?