Error creating index jahia_pages_data_index4

Hi.
In mysql it seems impossible to create the following index taken from your site's faq:
 
CREATE INDEX jahia_pages_data_index4 ON jahia_pages_def ( parentid_jahia_pages_data ) ;
 
This index should probably be created in table jahia_pages_data, as the column indicated is absent from table jahia_pages_def.
Regards.