Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Identifier a
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier t_logical_expressions_optimizer_low_cardinality
    Function and (children 1)
     ExpressionList (children 2)
      Function notEquals (children 1)
       ExpressionList (children 2)
        Identifier a
        Literal \'x\'
      Function notEquals (children 1)
       ExpressionList (children 2)
        Identifier a
        Literal \'y\'
    Set
