Re: Storing and fast retrieving of Email address

[Rick James]

What's the advantage of partitioning? The engine will still have to drill down a BTree to locate the desired page. No reduction in "seek time".

What's the advantage of changing from a varchar to an int? Well, one answer is if you have lots of other tables that use email address as a key. In that case, you are cluttering disk with copies of long keys, when you could have just a shorter key.

You question of WhatFunction(email) -- suggest MD5(). But you may as well do it in your application rather than shipping the email to/from Mysql.

The odds of a dup in md5 (or sha1) are sufficiently minuscule that it can be ignored.

Alternatively, you can use a lookup table to map between email and id:
CREATE TABLE email_map (
id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT,
email VARCHAR(...) NOT NULL,
PRIMARY KEY (id),
UNIQUE (email)
) ENGINE=InnoDB;

You could then use this via JOIN or subquery to do the necessary lookups coming and going.

Caveat: The mapping table works only if the string (email) is fits in the restriction (1K?) of how big an index can be. If you exceed that (say for images), the mapping table and its API becomes much more complicated. I have several techniques, none pretty.