Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Identifier metric.names
    TablesInSelectQuery (children 2)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier hourly
     TablesInSelectQueryElement (children 1)
      ArrayJoin (children 1)
       ExpressionList (children 1)
        Identifier metric
