Alias on union

[Eric Berryman]

I’m trying to use a union in a join, but I don’t see the alias as available
(I get an error that the alias/field does not exist on the line of the
below left join). The error shows available alias/fields and I see the
union id fields but the alias is an empty set aliases:[]. Is this possible?

Thank you!
Eric

List tableScans = new ArrayList<>();

for (String tableName : tablesToUnion) {
  RelNode tableScan = builder
    .scan(tableName)
    .project(builder.field("id"), builder.field("field1"))
   .build();
   tableScans.add(tableScan);
 }
 // Use pushAll to add all table scans to the stack and create a UNION ALL
builder.pushAll(tableScans);
RelNode union = builder.union(true, tableScans.size());

 // Start with the union as the initial part of the join
RelNode current = builder.push(union).as("core").build();

 // Iterate over the tables to join
for (String joinTable : tablesToJoin) {
  current = builder
     .push(current)
     .scan(joinTable)
     .join(JoinRelType.LEFT,
          builder.equals( builder.field(2, "core", "id"),
          builder.field(joinTable, "id")))
     .project(builder.fields())
     .build();
}