You can enter an outer join as a join override or as part of an override of the default query.
When you create a join override, the Designer appends the join override to the WHERE clause of the default query. During the session, the Integration Service translates the Informatica join syntax and includes it in the default query used to extract source data. When possible, enter a join override instead of overriding the default query.
When you override the default query, enter the join syntax in the WHERE clause of the default query. During the session, the Integration Service translates Informatica join syntax and then uses the query to extract source data. If you make changes to the transformation after creating the override, the Integration Service ignores the changes. Therefore, when possible, enter outer join syntax as a join override.