------字符串--》date类型
代码： select to_date(\'2014-12-19 10:00:00\', \'yyyy-mm-dd hh24:mi:ss\') as a,
to_date(\'2014/12/20 10:00:00\', \'yyyy/mm/dd hh24:mi:ss\') as b
from dual
SQL中不区分大小写，MM和mm被认为是相同的格式代码，所以Oracle的SQL采用了mi代替分钟。select to_date(\'2005-01-01 13:14:20\',\'yyyy-MM-dd HH24:mi:ss\') from dual;
date--->字符串
代码： select to_char(to_date(\'2014-12-19 10:05:00\', \'yyyy-mm-dd hh24:mi:ss\'),\'yyyy-mm-dd hh:mi:ss\') as a,
to_char(to_date(\'2014-12-19 10:05:00\', \'yyyy-mm-dd hh24:mi:ss\'),\'yyyy-mm-dd\') as b,
to_char(to_date(\'2014/12/20 10:00:00\', \'yyyy/mm/dd hh24:mi:ss\'),\'yy-mm-dd\')as c
from dual
格式可以自己选择
另：计算月末 月初
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本月月初：select trunc(to_date(\'20020221\',\'yyyymmdd\'),\'mm\') from dual;
下月月初：select trunc(add_months(to_date(\'20020221\',\'yyyymmdd\'),1),\'mm\') from dual;
如果只有年月，可以这样写，本月初：select to_date(\'200202\',\'yyyymm\') from dual;
下月月初:select add_months(to_date(\'200202\',\'yyyymm\'),1) from dual;
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本月月末：select last_day(\'20140201\')from dual;
下月月末：select last_day (add_months(\'20140201\',1))from dual
如果只有年月，可以这样写，本月月末：select add_months(to_date(\'201402\',\'yyyymm\')-1,1) from dual
下月 月末：select add_months(to_date(\'201402\',\'yyyymm\')-1,2) from dual