MySQL raises error 3028 when an ORDER BY inside a UNION references an aggregate function such as SUM or COUNT.
ER_AGGREGATE_ORDER_FOR_UNION (MySQL error 3028) occurs when the ORDER BY clause of a UNION query contains an aggregate like SUM(). Remove the aggregate, group first, or wrap the UNION in a subquery and sort outside to resolve the issue.
ER_AGGREGATE_ORDER_FOR_UNION
MySQL error 3028 appears when a UNION or UNION ALL query tries to sort the combined result set using an aggregate function in its ORDER BY clause.
The server rejects the statement because aggregates are calculated after ORDER BY in UNION processing, making such sorting logically ambiguous.
The error is triggered whenever ORDER BY includes functions like SUM(), COUNT(), AVG(), MIN(), or MAX() directly after a UNION block.
MySQL versions 5.7.5 and later enforce this rule to keep execution plans deterministic and standards-compliant.
Move the ORDER BY outside the UNION by wrapping the set operation in a subquery.
Alternatively, compute aggregates in a derived table, join back, and then sort. Removing the aggregate from ORDER BY also works if the exact ordering is not essential.
Report queries that UNION daily totals and then try to ORDER BY SUM(total) fail. Wrapping the UNION in a subquery and ordering outside restores functionality.
Ad-hoc analytics that UNION multiple SELECTs with COUNT(*) in ORDER BY must either GROUP BY first or sort by non-aggregate columns.
Always treat UNION output as a virtual table. Apply ORDER BY and LIMIT only after the full set is materialised.
Use Galaxy’s query linter to detect aggregates in ORDER BY within UNION blocks before execution.
ER_ORDER_BY_AGGREGATE (1583) appears in non-UNION queries when ORDER BY contains aggregates without GROUP BY.
ER_FIELD_IN_ORDER_NOT_SELECT (3065) occurs when ORDER BY references a column not present in SELECT. Both issues resolve by adjusting ORDER BY or using derived tables.
Including SUM(), COUNT(), or other aggregate functions directly in the ORDER BY list following a UNION statement.
Migrating to MySQL 5.7.5+ where stricter parsing detects invalid ORDER BY usage that older versions allowed.
Ad-hoc queries copied between tools often add ORDER BY SUM(x) without realising a UNION appears earlier.
Raised when ORDER BY contains an aggregate without GROUP BY in non-UNION queries.
Occurs if ORDER BY references a column not in the SELECT list when ONLY_FULL_GROUP_BY is active.
Triggered when a non-aggregated column in SELECT is not included in GROUP BY under strict mode.
No configuration parameter bypasses ER_AGGREGATE_ORDER_FOR_UNION. You must rewrite the query.
Both UNION and UNION ALL raise error 3028 because ordering rules are identical.
Yes. Creating a view or derived table and then selecting from it lets you apply ORDER BY safely.
Galaxy’s static analysis flags aggregates in ORDER BY within UNION queries and suggests subquery rewrites before you run the SQL.
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