SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 4)
   ExpressionList (children 1)
    Identifier replication_lag
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier system.clusters
   Function in (children 1)
    ExpressionList (children 2)
     Identifier cluster
     Literal Tuple_(\'rdb1\', \'rdb2\')
   ExpressionList (children 2)
    OrderByElement (children 1)
     Identifier cluster
    OrderByElement (children 1)
     Identifier replica_num
