New Query Layer: Union

[JasonMoore]

Is it possible to make a New Query Layer which combines multiple feature classes usin the Union command?

I can get it to bring all the attributes from the layer into a table, but when I add the SHAPE field to the query I get an error.

Underlying DBMS error[ORA-01405: fetched column value is NULL]

I am using ArcGIS10.2 on an Oracle SDE database.  The schema for all five feature classes are the same.

[Bud]

I know this post is ancient. But to anyone who has the same problem: you could try running the same UNION query in an SQL client like Toad or SQL Developer (Oracle) to see if you get the same error there. If you do, then it’s likely a problem with your SQL. If not, then it means the problem is probably in ArcGIS Pro. 
That approach might be useful for narrowing down the root cause.

[JoelBennett]

I ran into this today, and solved the problem by using UNION ALL instead of UNION, because I didn't have to worry about duplicate records, which was an impossible situation in this case.  At a high level, the problem occurred because a record had a SHAPE value of NULL.