SQL 'like' vs '=' performance

Question

It would seem that in general '=' is faster than 'like' when using wildcards. This appears to be the conventional wisdom. However, lets suppose I have a column containing a limited number of different fixed, hardcoded, varchar identifiers, and I want to select all rows matching one of them:

select * from table where value like 'abc%'

and

select * from table where value = 'abcdefghijklmn'

'Like' should only need to test the first three chars to find a match, whereas '=' must compare the entire string. In this case it would seem to me that 'like' would have an advantage, all other things being equal.

This is intended as a general, academic question, and so should not matter which DB, but it arose using SQL Server 2005.

Answer 1

Using '=' operator is faster than the LIKE operator in comparing strings because '=' operator compares the entire string but the LIKE keyword compares by each character of the string. We can use LIKE to check a particular pattern like column values starting with 'abc' in this case. You can use equal (=) operator if you are looking for a specific observation like 'abcdefghijklmn' in this case.

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