I am trying to add views using MM02.  It is showing me just 3 views ...BASIC DATA1, BASIC DATA2 &  CLASSIFICATION..... I want to add other views but am not able to do it.

There are 2 ways to add views to the existing material master:

1.  Go to mm01 
    - Enter the material for which you want to add the views. 
    - Then you enter the same material in copy from material 
    - Then you may find all the view 
    - Then select the views you want to add and make entries in the same view and save it 
    All this is done in mm01.

or

    You can mass extend views for a material in tcode mm50. 
    Select the maintenance status as V for e.g. if you want to add views of sales.  *-- Chirag

2. If the default setting is done in the material of the material type then you may not find the new views in mm01 
    If that is the case, then you go to spro  >> log general >> mat master >> basic sett >> material  types >> 
    define attributes of materisl types.
    - Select material type of the material in which you want to make the change
    - Double click on the same, then on right hand side, you will find user parameters under which you will find the views 
    - Select the view you want and save your settings
    - Then go to mm01 and do the way it is mentioned in the first step.                  *-- Praveen Garg

Download this Material Type documents for the step by step guide on Step 2:
Configuring the SAP Material Master Material Type

Why we are maintaining 4 views for mrp? What is the reason behind that? 

The 4 MRP views that we maintain has got its individual importance like in 
- MRP1 - For for consumption based planning
- MRP2 - Procurement type (inhouse or external)
- MRP3 - For Planning strategy & consumption period
- MRP4 - For repetitive mfg.

It is not mandatory to maintain all MRP views.  It depends upon your company profile.      *-- Rugved Dixir 

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