anchor.diff:      ;
   
   subquery
  -    : LP_ unionSelect RP_
  -    ;
  +    : LP_ unionClause_ RP_
  +    ;
  
positive.code:     ;
  
  select 
      : withClause_? unionSelect
      ;
  
  withClause_
  
negative.code:     : ignoredIdentifier_ columnNames? AS subquery
      ;
  
  unionClause_
      : selectExpression (UNION (ALL | DISTINCT)? selectExpression)*
      ;
  
  