Oracle查询数据，按月统计，生成默认数据和月份【今年和去年的月份】

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select to_char(add_months(start_date, (level - 1)), 'yyyymm') stat_date,
       0 as kw_num
  from (select add_months(trunc(sysdate, 'y'), -12) as start_date,
               add_months(trunc(sysdate, 'y'), 12) as end_date
          from dual)
connect by level < = months_between(end_date, start_date)