利用伪列算出每个月那几天是星期天(ORACLE)

1.首先我们要用到LEVEL .... CONNECT BY level是一个伪列,类似于rownum,而后面加connect by则可以构造出一个循环来; 例如: SQL>select level from dual connect by level<=5; 结果 ----------------------------------------------- LEVEL   1   2   3   4   5 一个伪列并循环显示就这样产生了. 2.接着我要构造出一个日期的伪列出来,需要用到日期函数,比如现在是12月,我需要构造出来2007年12月1日----2007年12月31日的伪列. SQL>select last_day(sysdate) from dual; 结果 ----------------------------------------------- 1       2007-12-31 1:22:24 SQL>select to_char(last_day(sysdate),'DD') from dual; 结果 ----------------------------------------------- 1       31 SQL>select level from dual connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 SQL>select TRUNC(SYSDATE,'MM') from dual; 结果 ----------------------------------------------- 1       2007-12-1 接着我们要做的事情就是把上面的函数结合起来实现2007年12月1日----2007年12月31日的伪列 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 2007-12-1 2 2007-12-2 3 2007-12-3 4 2007-12-4 5 2007-12-5 6 2007-12-6 7 2007-12-7 8 2007-12-8 9 2007-12-9 10 2007-12-10 11 2007-12-11 12 2007-12-12 13 2007-12-13 14 2007-12-14 15 2007-12-15 16 2007-12-16 17 2007-12-17 18 2007-12-18 19 2007-12-19 20 2007-12-20 21 2007-12-21 22 2007-12-22 23 2007-12-23 24 2007-12-24 25 2007-12-25 26 2007-12-26 27 2007-12-27 28 2007-12-28 29 2007-12-29 30 2007-12-30 31 2007-12-31 3.构造出日期伪列后，我们只需要加上一个where条件既可以查询出这个月的星期日都是几号了 SQL>select to_char(sysdate,'DAY') from dual; 结果 ----------------------------------------------- 1 星期六 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual SQL>where to_char(TRUNC(SYSDATE,'MM')-1+level,'DAY') = '星期日' SQL>connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 2007-12-2 2 2007-12-9 3 2007-12-16 4 2007-12-23 5 2007-12-30 也可以把sql语句换成 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual SQL>where to_char(TRUNC(SYSDATE,'MM')-1+level,'D') = 1 SQL>connect by level<=to_char(last_day(sysdate),'DD'); 1.首先我们要用到LEVEL .... CONNECT BY level是一个伪列,类似于rownum,而后面加connect by则可以构造出一个循环来; 例如: SQL>select level from dual connect by level<=5; 结果 ----------------------------------------------- LEVEL   1   2   3   4   5 一个伪列并循环显示就这样产生了. 2.接着我要构造出一个日期的伪列出来,需要用到日期函数,比如现在是12月,我需要构造出来2007年12月1日----2007年12月31日的伪列. SQL>select last_day(sysdate) from dual; 结果 ----------------------------------------------- 1       2007-12-31 1:22:24 SQL>select to_char(last_day(sysdate),'DD') from dual; 结果 ----------------------------------------------- 1       31 SQL>select level from dual connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 SQL>select TRUNC(SYSDATE,'MM') from dual; 结果 ----------------------------------------------- 1       2007-12-1 接着我们要做的事情就是把上面的函数结合起来实现2007年12月1日----2007年12月31日的伪列 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 2007-12-1 2 2007-12-2 3 2007-12-3 4 2007-12-4 5 2007-12-5 6 2007-12-6 7 2007-12-7 8 2007-12-8 9 2007-12-9 10 2007-12-10 11 2007-12-11 12 2007-12-12 13 2007-12-13 14 2007-12-14 15 2007-12-15 16 2007-12-16 17 2007-12-17 18 2007-12-18 19 2007-12-19 20 2007-12-20 21 2007-12-21 22 2007-12-22 23 2007-12-23 24 2007-12-24 25 2007-12-25 26 2007-12-26 27 2007-12-27 28 2007-12-28 29 2007-12-29 30 2007-12-30 31 2007-12-31 3.构造出日期伪列后，我们只需要加上一个where条件既可以查询出这个月的星期日都是几号了 SQL>select to_char(sysdate,'DAY') from dual; 结果 ----------------------------------------------- 1 星期六 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual SQL>where to_char(TRUNC(SYSDATE,'MM')-1+level,'DAY') = '星期日' SQL>connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 2007-12-2 2 2007-12-9 3 2007-12-16 4 2007-12-23 5 2007-12-30 也可以把sql语句换成 SQL>select TRUNC(SYSDATE,'MM')-1+level from dual SQL>where to_char(TRUNC(SYSDATE,'MM')-1+level,'D') = 1 SQL>connect by level<=to_char(last_day(sysdate),'DD'); 结果 ----------------------------------------------- 1 2007-12-2 2 2007-12-9 3 2007-12-16 4 2007-12-23 5 2007-12-30 数字1-7分别代表星期天到星期六; OK到此分析完毕,Oracle的伪列的功能还是很不错的呀！~呵呵 结果 ----------------------------------------------- 1 2007-12-2 2 2007-12-9 3 2007-12-16 4 2007-12-23 5 2007-12-30 数字1-7分别代表星期天到星期六; OK到此分析完毕,Oracle的伪列的功能还是很不错的呀！~呵呵