> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/server/reference/error-codes/mariadb-error-codes-3000-to-3099/e3028.md).

# Error 3028: Expression of ORDER BY contains aggregate function and applies to a UNION

| Error Code | SQLSTATE | Error                            | Description                                                                   |
| ---------- | -------- | -------------------------------- | ----------------------------------------------------------------------------- |
| 3028       |          | ER\_AGGREGATE\_ORDER\_FOR\_UNION | Expression #%u of ORDER BY contains aggregate function and applies to a UNION |

## Possible Causes and Solutions

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