MySQL error: key specification without a key length

Question

I have a table with a primary key that is a varchar(255). Some cases have arisen where 255 characters isn\'t enough. I tried changing the field to a text, but I get the foll

Answer 1

Another excellent way of dealing with this is to create your TEXT field without the unique constraint and add a sibling VARCHAR field that is unique and contains a digest (MD5, SHA1, etc.) of the TEXT field. Calculate and store the digest over the entire TEXT field when you insert or update the TEXT field then you have a uniqueness constraint over the entire TEXT field (rather than some leading portion) that can be searched quickly.