Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 1)
    ExpressionList (children 1)
     Function regexp_replace (children 1)
      ExpressionList (children 3)
       Function identity (children 1)
        ExpressionList (children 1)
         Literal \'abc123\'
       Literal \'^abc\'
       Literal \'\'
