获取当前月份的每一天的数据

oracle

SELECT TO_DATE(TO_CHAR(SYSDATE, 'YYYYMM'), 'YYYYMM') + (ROWNUM - 1) DAY_ID 
  FROM DUAL 
CONNECT BY ROWNUM <= 
           TO_NUMBER(TO_CHAR(LAST_DAY(TO_DATE(TO_CHAR(SYSDATE, 'YYYYMM'), 
                                              'YYYYMM')), 
                             'DD')) 

mysql

SELECT 
  DATE_ADD(CURDATE(),INTERVAL(CAST(help_topic_id AS SIGNED INTEGER)-(DAYOFMONTH(CURDATE())-1)) DAY) DAY 
FROM mysql.help_topic 
WHERE help_topic_id < DAY(LAST_DAY(CURDATE())) 
ORDER BY help_topic_id 

备注：help_topic 为 mysql 存储内置函数的表