SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 1)
    Function least (children 1)
     ExpressionList (children 2)
      Identifier value
      Literal UInt64_0
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier system.metrics
   Function equals (children 1)
    ExpressionList (children 2)
     Identifier metric
     Literal \'MemoryTracking\'