Using LIKE vs. = for exact string match

Question

First off, I recognize the differences between the two:
- Like makes available the wildcards % and _
- significant trailing whitespace
- colation issues

Answer 1

In a decent DBMS, the DB engine would recognise that there were no wildcard characters in the string and implicitly turn it into a pure equality (not necessarily the same as =). So, you'd only get a small performance hit at the start, usually negligible for any decent-sized query.

However, the MySQL = operator doesn't necessarily act the way you'd expect (as a pure equality check). Specifically, it doesn't by default take into account trailing spaces for CHAR and VARCHAR data, meaning that:

SELECT age WHERE name = 'pax'

will give you rows for 'pax', 'pax' and 'pax'.

If you want to do a proper equality check, you use the binary keyword:

SELECT field WHERE name = binary 'pax'

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You can test this with something like:

mysql> create table people (name varchar(10));

mysql> insert into people value ('pax');
mysql> insert into people value ('pax ');
mysql> insert into people value ('pax  ');
mysql> insert into people value ('pax   ');
mysql> insert into people value ('notpax');

mysql> select count(*) from people where name like 'pax';
1

mysql> select count(*) from people where name = 'pax';
4

mysql> select count(*) from people where name = binary 'pax';
1