MySQL: How to alter varchar(255) UNIQUE column to UNIQUE Text NOT NULL?

Question

The current column is a VARCHAR(255) NOT NULL, so how do I change it to TEXT NOT NULL?

NOTE: The column intended to be changed its property type is a UNIQUE KEY comb

Answer 1

I had exactly the same problem.

I added a new char(32) column (I called it hash and added a unique index on it) and two triggers.

delimiter | 

CREATE TRIGGER insert_set_hash
    BEFORE INSERT ON my_table_name
    FOR EACH ROW BEGIN  
          SET NEW.hash = MD5(NEW.my_text);
    END; |

CREATE TRIGGER update_set_hash
    BEFORE UPDATE ON my_table_name
    FOR EACH ROW BEGIN  
           SET NEW.hash = MD5(NEW.my_text);
    END; |


delimiter ;

By using the triggers and adding a UNIQUE index on hash you can be sure that the hash values will always be up-to-date and unique.