Explain EXPLAIN PIPELINE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 6)
    ExpressionList (children 2)
     Identifier a
     Function count (children 1)
      ExpressionList
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier dist_t_different_dbs
    ExpressionList (children 1)
     Identifier a
    ExpressionList (children 1)
     OrderByElement (children 1)
      Identifier a
    Literal UInt64_500
    Literal UInt64_5
