Change Varchar data type to primary key

Question

Hello i am curently trying to set up a data base in MYSQL and i want to have my Varchar element as the Primary Key but it always gives me an error like this:

Invalid use of NULL value

the command i am using is:

ALTER  TABLE temp_keys ADD PRIMARY KEY (temp_key);

and here is how the table is set up:

Intel

I hope that some one of you can help me with this.

Answer 1

VARCHAR data type is not a problem. PRIMARY KEY columns must be defined as NOT NULL. Append CHANGE temp_key temp_key VARCHAR (50) NOT NULL in your query and change value(50) according to your need.

Just execute ALTER TABLE temp_keys CHANGE temp_key temp_key VARCHAR (50) NOT NULL, ADD PRIMARY KEY (temp_key);