Set unique from Control Centre

[Paul Wallace]

Hi, 
        Using MYSQL Control Centre 0.9.4 Beta, I would like to set a
column to be a unique field. When I choose to edit the table, the Unique
radio, along with Index and Fulltext is dulled out (deactivated). No
amount of 'fiddling' has enabled me to select this feature. 
         How may I select a column to be unique using the said version
please? 
 
thanks
 
Paul.