Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Identifier t.a
    TablesInSelectQuery (children 2)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test
     TablesInSelectQueryElement (children 1)
      ArrayJoin (children 1)
       ExpressionList (children 1)
        Identifier arr
