Medium
SQL-W07sqlFirst Purchase Per User
Problem
Given `purchases(user_id, ts, item)`, output one row per user with their **first-ever** item and ts. Use a window function (FIRST_VALUE / ROW_NUMBER), not GROUP BY.
Input
purchases
Output
user_id, first_ts, first_item
Constraints
1 ≤ rows ≤ 10^6
Sample input
see prompt
Sample output
...
Explanation
ROW_NUMBER PARTITION BY user_id ORDER BY ts → keep rn = 1.
window-fnfirst-valuededuplicate@Doordash
Visible test cases
in: see
out: ...
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