MySQL - Fast indexing
Some examples of setting up indices in MySQL are given
Setting up fast indices in MySQL SUGGESTION #1 : Standard Indexing

CREATE TABLE mytable
(
    id int not null auto_increment,
    myfield varchar(255) not null,
    primary key (id),
    key (myfield)
);

If you index like this, you can either look for the whole string or do left-oriented LIKE searches

SUGGESTION #2 : FULLTEXT Indexing

CREATE TABLE mytable
(
    id int not null auto_increment,
    myfield varchar(255) not null,
    primary key (id),
    fulltext (myfield)
);

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