mysql binary comparison doesnt use index

Question

I have the following query:

EXPLAIN EXTENDED SELECT *
FROM (
`photo_data`
)
LEFT JOIN `deleted_photos` ON `deleted_photos`.`photo_id` = `photo_data`.`photo_id`
WHERE photo_data.photo_id = 'UKNn'
AND `deleted_photos`.`photo_id` IS NULL

I unfortunately have to use binary to compare this photo_id (which is being handed to me from a different outside service). So that I avoid 'uknn' being pulled out of the datbase instead of 'UKNn'.

The problem is that when I do the explain, i see the use of binary doesn't use the index. If I take out binary it uses the index for photo_id. Is there a way to be able to use the binary option and use an index with it?

Answer 1

If you need just to compare field value in case-sensitive manner - you could change collation for that field specifically.

ALTER TABLE photo_data MODIFY photo_id VARCHAR(5) CHARACTER SET utf8 COLLATE utf8_bin

or

ALTER TABLE photo_data MODIFY photo_id VARCHAR(5) CHARACTER SET utf8 COLLATE utf8_general_cs

Answer 2

MySQL uses the collation of the column for the index. An index with a non-binary collation isn't useful for a binary lookup since the order might be different.

You could change the column itself to binary collation:

ALTER TABLE YourTable MODIFY
   YourColumn VARCHAR(4)
   CHARACTER SET latin1
   COLLATE latin1_bin;

Then the index would be useful for a binary lookup.