数据库计算日期，统计系统时间（月）的数据   计算出本月第一天到最后一天的日期：   www.2cto.com   select  date(rtrim(char(year(min(start_time))))||'-'||rtrim(char(month(min(start_time))))||'-1') as startTime,   date(rtrim(char(year(max(start_time))))||'-'||rtrim(char(month(max(start_time)+1 month)))||'-1') as endTime from table_A   t;   统计本月数据： select sum(MONTHLY_REPAYMENTS) as totle from TABLE_A   where ID='123'   AND  date('2012-11-01') <  date(current timestamp  )  and  date('2012-12-01') > date(current timestamp)