A Query Activity in an Automation can fail for several reasons, including:
* The query takes more than 60 minutes to run (A)- Long-running queries are subject to timeouts, which can cause the query to fail.
* The query results in duplicate rows not allowed by the primary key (C)- If the query attempts to insert duplicate rows into a data extension that has a primary key constraint, it will fail.
* The query is inserting a value that is larger than the size of a field (E)- If the query attempts to insert data that exceeds the field size limits, it will result in an error.
References:
* Salesforce Marketing Cloud Query Activity
* Salesforce Marketing Cloud SQL Best Practices