Question

Write a SELECT statement that returns the same result set as this SELECT statement, but don’t use a join. Instead, use a subquery in a WHERE clause that uses the IN keyword. SELECT DISTINCT category_name

Answer 1

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Explanation:

The complete question is

Write a SELECT statement that returns the same result set as this SELECT statement, but don't use a

join. Instead, use a subquery in a WHERE clause that uses the IN keyword.

SELECT DISTINCT category_name

FROM categories c JOIN products p

ON c.category_id = p.category_id

ORDER BY category_name

The join clause  gives us all the registers of both tables, for which the category_id of categories coincides to  the category_id in the table products. That is, we can first select the distinct category_id's from products and the see the categories from categories table, whose id is in that list. That means writing the following query:

Select distinct category_name

from categories c

where c.category_id in (

select distinct p.category_id

from products p)

order by category_name