63. UNION ALL vs UNION: Counting Logins
MediumSet OperationsUNION ALLUNIONduplicatesCOUNT
UNION ALL keeps duplicates; UNION removes them. The difference is observable: stack two login logs and count the rows each way.
Task: report two counts in a single row — the number of rows when combining the two logs with UNION ALL (duplicates kept) and with UNION (distinct users).
Return columns all_count, distinct_count. Single row.
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