Distinct product categories per order

Join order_items to products and list each order's distinct product categories as one string, alphabetically, separated by a bare comma with no space (","). Columns: order_id, categories. Sort by order_id.

Tables & sample data

order_items

11 rows total · first 5 shown

order_idvarchar	product_idvarchar	qtybigint	unit_pricebigint
o_001	p_003	3	20
o_001	p_005	1	40
o_002	p_001	1	200
o_003	p_003	1	20
o_003	p_004	1	30

products

6 rows total · first 5 shown

product_idvarchar	categoryvarchar	list_pricebigint
p_001	electronics	500
p_002	electronics	150
p_003	books	20
p_004	books	35
p_005	clothing	45

query.sql

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