Explain EXPLAIN AST (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 1)
    ExpressionList (children 1)
     Function isNotDistinctFrom (children 1)
      ExpressionList (children 2)
       Literal \'x\'
       Function concat (children 1)
        ExpressionList (children 2)
         Literal \'x\'
         Literal \'a\'
