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