Use '=' or LIKE to compare strings in SQL?

Question

There's the (almost religious) discussion, if you should use LIKE or '=' to compare strings in SQL statements.

• Are there reasons to use LIKE?
• Are there reasons to use '='?
• Performance? Readability?

Answer 1

LIKE and the equality operator have different purposes, they don't do the same thing:
= is much faster, whereas LIKE can interpret wildcards. Use = wherever you can and LIKE wherever you must.

SELECT * FROM user WHERE login LIKE 'Test%';

Sample matches:

TestUser1
TestUser2
TestU
Test

Answer 2

To see the performance difference, try this:

SELECT count(*)
FROM master..sysobjects as A
JOIN tempdb..sysobjects as B
on A.name = B.name

SELECT count(*)
FROM master..sysobjects as A
JOIN tempdb..sysobjects as B
on A.name LIKE B.name

Comparing strings with '=' is much faster.

Answer 3

In my small experience:

"=" for Exact Matches.

"LIKE" for Partial Matches.

Answer 4

There's a couple of other tricks that Postgres offers for string matching (if that happens to be your DB):

ILIKE, which is a case insensitive LIKE match:

select * from people where name ilike 'JOHN'

Matches:

• John
• john
• JOHN

And if you want to get really mad you can use regular expressions:

select * from people where name ~ 'John.*'

Matches:

• John
• Johnathon
• Johnny

Answer 5

Just as a heads up, the '=' operator will pad strings with spaces in Transact-SQL. So 'abc' = 'abc ' will return true; 'abc' LIKE 'abc ' will return false. In most cases '=' will be correct, but in a recent case of mine it was not.

So while '=' is faster, LIKE might more explicitly state your intentions.

http://support.microsoft.com/kb/316626

Answer 6

For pattern matching use LIKE. For exact match =.

Answer 7

LIKE is used for pattern matching and = is used for equality test (as defined by the COLLATION in use).

= can use indexes while LIKE queries usually require testing every single record in the result set to filter it out (unless you are using full text search) so = has better performance.

Answer 8

There is another reason for using "like" even if the performance is slower: Character values are implicitly converted to integer when compared, so:

declare @transid varchar(15)

if @transid != 0

will give you a "The conversion of the varchar value '123456789012345' overflowed an int column" error.

Answer 9

LIKE does matching like wildcards char [*, ?] at the shell
LIKE '%suffix' - give me everything that ends with suffix. You couldn't do that with =
Depends on the case actually.