[SQL] Joining tables when values are missing

I have the following query to get the names of categories and subcategories for items given by an ID:

SELECT a.value, b.value FROM X a
INNER JOIN X b ON a.ID = a.ID
AND a.NAME = 'Category'
AND b.NAME = 'Subcategory'


The issue is that sometimes my categories do not have any subcategories. In that case, there is no row for Subcategory for that ID. Removing b.NAME = 'Subcategory' is not really an option either since there are over fifty distinct values for X.NAME. Do I have any other option than creating an X.NAME = 'Subcategory' with X.value = NULL in cases subcategory is missing?

So, I want a query which returns the Category and a NULL value when subcategory is missing.

Here's some sample data:

insert into X values ('10101', 'Category', 'Murder');
insert into X values ('10101', 'Subcategory', 'Strangulation');
insert into X values ('15151', 'Category', 'Theft');
insert into X values ('15151', 'Subcategory', 'Vehical');
insert into X values ('15151', 'Severity', 'High');
insert into X values ('33456', 'Category', 'Theft');
insert into X values ('45565', 'Category', 'Murder');
insert into X values ('45565', 'Severity', 'Low');
insert into X values ('76543', 'Category', 'Violence');
insert into X values ('76543', 'Subcategory', 'Domestic Violence');
insert into X values ('76543', 'Severity', 'Medium');

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