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Ch9 (Joins and unions (unions (to accesss more observations, assumption…

- - - - combines two
        
        data ets
        
        with
        
        shared ID value
        
        two types of join
        
        2 more items...
  - - - multiple ccollumns are in common
        
        ex
        
        companhy has multiple cust
        
        multiple databases
        
        union will create
        
        one table
        
        1 more item...
- - - - designed
        
        not to accepot order
        
        unless an customer
        
        account
        
        exists