Error 42803 (grouping_error) occurs when a SELECT query references columns that are neither grouped nor aggregated.
PostgreSQL error 42803 (grouping_error) occurs when a non-aggregated column is selected without appearing in the GROUP BY list. Add the column to GROUP BY or wrap it in an aggregate function to fix the issue.
PostgreSQL Error 42803
Error 42803 indicates a grouping_error. PostgreSQL throws it when a SELECT statement mixes grouped data with columns that are neither aggregated nor listed in the GROUP BY clause.
The planner cannot decide how to collapse ungrouped columns into a single result row, so it stops execution and surfaces the error.
Fixing it is essential because it prevents incomplete or misleading aggregations from reaching production code.
Omitting a non-aggregated column from the GROUP BY list is the direct trigger.
PostgreSQL enforces ANSI SQL rules that every column in the SELECT list must be either part of an aggregate function or named in GROUP BY.
Using DISTINCT with GROUP BY, nested subqueries that reference outer columns incorrectly, and window functions mixed with aggregation can also surface the error.
Add every non-aggregated column to the GROUP BY clause.
Alternatively, wrap the column in an aggregate such as MAX(), MIN(), COUNT(), or use DISTINCT ON.
Validate derived tables and CTEs. Make sure their SELECT lists obey the same rule before they are joined or unioned higher up the query.
Selecting id, name, and COUNT(*) without grouping by id and name triggers the error.
Adding GROUP BY id, name resolves it.
Joining an aggregated subquery with a table and projecting a column from the outer table that is not grouped also causes the error. Restructure the query so aggregation happens after the join or aggregate the missing column.
Always cross-check the SELECT list against the GROUP BY clause during code review.
Use code linters or Galaxy’s real-time validator to surface mismatches instantly.
Favor CTEs for complex aggregations so each stage has clear grouping boundaries. Unit-test queries that evolve frequently to catch grouping issues early.
Error 42830 (invalid_foreign_key) appears when foreign keys mismatch referenced columns. It differs because it concerns referential integrity, not aggregation.
Error 42P10 (invalid_column_reference) is thrown when a column is ambiguous. While also a SELECT-list problem, the fix involves qualifying column names instead of grouping.
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The rule guarantees deterministic results. Without grouping or aggregation, PostgreSQL cannot decide which value to return for each ungrouped column.
No. The SQL standard requires it. PostgreSQL enforces the rule to maintain data integrity.
Yes, if any value is acceptable. Pick the aggregate that matches your semantic need. Otherwise, redesign the query.
Galaxy’s AI copilot and linter flag ungrouped columns instantly and suggest adding them to GROUP BY or wrapping them in aggregates.
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