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

You should define which leading portion of a TEXT column you want to index.

InnoDB has a limitation of 768 bytes per index key and you won't be able to create an index longer than that.

This will work fine:

CREATE TABLE t_length (
      mydata TEXT NOT NULL,
      KEY ix_length_mydata (mydata(255)))
    ENGINE=InnoDB;

Note that the maximum value of the key size depends on the column charset. It's 767 characters for a single-byte charset like LATIN1 and only 255 characters for UTF8 (MySQL only uses BMP which requires at most 3 bytes per character)

If you need your whole column to be the PRIMARY KEY, calculate SHA1 or MD5 hash and use it as a PRIMARY KEY.