Explain EXPLAIN SYNTAX (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 3)
    ExpressionList (children 2)
     Function plus (children 1)
      ExpressionList (children 2)
       Identifier x1
       Identifier x3
     Identifier x3
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test
    ExpressionList (children 2)
     Literal UInt64_1
     Literal UInt64_2