Find Values Owned Only by the Selected User

Find the values associated with a chosen user that are not associated with any other user.

Input Tables

user_values

Column	Type	Meaning
row_id	INTEGER	Primary key
user_id	INTEGER	Non-null user identifier
item_value	TEXT	Non-null value associated with that user

selected_user contains exactly one row with one non-null INTEGER column, user_id.

These tables are an explicit relational representation of a mapping from users to their values. A user may have repeated rows for the same value.

Output Contract

Write one read-only PostgreSQL query returning a single column, item_value. Return each value owned by the selected user exactly once only if no different user owns that value. Sort values ascending. Compare values exactly as stored.

Example

selected_user contains user_id = 10.

row_id	user_id	item_value
1	10	apple
2	10	pear
3	10	pear
4	20	apple
5	30	plum

Expected result:

item_value
pear

Constraints and Clarifications

• Repeated ownership by the selected user does not disqualify a value.
• Ownership by even one different user disqualifies it.
• A selected user with no values produces no rows.
• Values are nonempty lowercase English strings; there are no null values.

Hint: Separate repetition from shared ownership

Several rows for one user are different from a matching row for another user. Check the identity of the owner when excluding shared values.

Values Owned Only by the Selected User

Table user_values

column	type	constraints
row_id	INTEGER	PRIMARY KEY
user_id	INTEGER	NOT NULL
item_value	TEXT	NOT NULL

Sample data:

item_value	row_id	user_id
kiwi	1	42
apple	2	42
mango	3	42
mango	4	42
apple	5	17
banana	6	42
banana	7	23
banana	8	23
cherry	9	17
cherry	10	23
grape	11	42
grapefruit	12	17
lemon	13	58
fig	14	42
lemon	15	58

Table selected_user

column	type	constraints
user_id	INTEGER	NOT NULL

Sample data:

user_id
42

Expected output

item_value
fig
grape
kiwi
mango

Hints

1. Separate repetition from shared ownership: several rows for one user are different from a matching row for another user. Check the identity of the owner when excluding shared values.