Method is_union

sql/sql_lex.h:1011–1015

typedef class st_select_lex SELECT_LEX;

inline bool st_select_lex_unit::is_union ()
{ 
  return first_select()->next_select() && 
    first_select()->next_select()->linkage == UNION_TYPE;
}

/// Utility RAII class to save/modify/restore a Resolve_place
class Switch_resolve_place