Find all other records for an ID if a record exists

I need to find all other related records for an ID if a certain value exists.

I have almost no SQL experience and work primarily on a front end design UI, rather than writing the code myself.

The basic query is:

For a given period, if any customer placed an order in that period, I’d like to see all orders for those customers.

So looking for all orders for any customer who placed an order in April:

Customer Order   Month
John     Apples  January
John     Pears   January
John     Oranges February
John     Bananas April
Amy      Apples  March
Amy      Pears   May
Amy      Oranges July
Amy      Bananas September
Larry    Apples  January
Larry    Pears   April
Larry    Oranges August
Larry    Bananas November
Marge    Apples  April
Marge    Pears   May
Marge    Oranges June
Marge    Bananas July

Expected result would be:

Customer Order   Month
John     Apples  January
John     Pears   January
John     Oranges February
John     Bananas April
Larry    Apples  January
Larry    Pears   April
Larry    Oranges August
Larry    Bananas November
Marge    Apples  April
Marge    Pears   May
Marge    Oranges June
Marge    Bananas July

Any help provided would be greatly appreciated.

Answer

I would write it literally like your described it: Find all the customers from April and then show all the orders for those customers.

SELECT * FROM OrderTable ot WHERE ot.Customer IN 
    (SELECT DISTINCT Customer FROM OrderTable WHERE Month = 'April')