mysql - efficient database design inheritance -

i want design database have 2 categories. there 2 subcategories in each category, similar other category like:

preventive equipment maintenance:

• cat1
  • id, equipment,model, series, accesories,date, cost, status
• cat 2
  • id, equipment,model, series, accesories,date, cost, status

corrective equipment maintenance

• cat1
  • id, new equipment, old equipment, borreowed equipment, description
• cat 2
  • id, new equipment,model, series, accesories,date, cost, old equipment, borreowed equipment, description

so can see diference between data collected on preventive equipment maintenance cat (either cat1 or cat2). solve thought make table like

create table `preventive_e`(       id          integer  not null primary key,       equipment   varchar(25) ,       cat         varchar(4) ,             constraint `uc_info_e` unique (`id`)            ); insert `preventive_e` values (1,'nintendo','cat1'); insert `preventive_e` values (2,'psp','cat2'); 

now in corrective same, not same fields, same fields, if cat1 want store fields, if cat 2 want store same fields more fields

is there way use inheritance or something?, extending fields being able add more particular fields? how query like.

sqlfiddle

why not call table generic both equipment_maint , have column acting flag it's usage.

fiddle

create table `equipment_maint`(   id          integer  not null primary key,   equipment   varchar(25)  ,   cat         varchar(50) ,     type       varchar(20),  /* usage on type of maintenance */   constraint `uc_info_e` unique (`id`)            );