數字函數：
ROUND按指定小數位 四捨五入
TRUNC按指定小數位 截斷
MOD兩數相除，取餘
4 5 6 . 7 8 9
-3 -2 -1 0 1 2 3
round(456.789,2)-->9>4-->456.79
trunc(456.789,2)-->----->456.78
round(456.789,-2)-->5>4-->500
round(456.789,-1)-->6>4-->460
SQL> select round(456.789,-1) from dual;
ROUND(456.789,-1)
-----------------
460
SQL> select round(456.789,-2) from dual;
ROUND(456.789,-2)
-----------------
500
SQL>
SQL> select mod(456,2) from dual;
MOD(456,2)
----------
0
SQL> select mod(457,2) from dual;
MOD(457,2)
----------
1
SQL>
SQL> select abs(-100) from dual; #絕對值
ABS(-100)
----------
100
日期函數
DD-MON-RR
SQL> select sysdate from dual;
SYSDATE
---------
10-APR-17
SQL>
SQL> select to_char(sysdate,'yyyy-mm-dd') from dual;
TO_CHAR(SY
----------
2017-04-10
SQL>
修改日期顯示格式
SQL> select hiredate from emp where deptno=10;
HIREDATE
---------
09-JUN-81
17-NOV-81
23-JAN-82
SQL> show parameter nls_date_format
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
nls_date_format string
SQL> alter session set nls_date_format='yyyy-mm-dd';
Session altered.
SQL> select hiredate from emp where deptno=10;
HIREDATE
----------
1981-06-09
1981-11-17
1982-01-23
SQL>
SQL> select sysdate-hiredate,ename from emp;
SYSDATE-HIREDATE ENAME
---------------- ----------
13263.7462 SMITH
13198.7462 ALLEN
13196.7462 WARD
SQL> select sysdate-1,ename from emp;
SYSDATE-1 ENAME
---------- ----------
2017-04-09 SMITH
2017-04-09 ALLEN
2017-04-09 WARD
2017-04-09 JONES
2017-04-09 MARTIN
SQL> select ename,months_between(sysdate,hiredate) months from emp;
ENAME MONTHS
---------- ----------
SMITH 435.798359
ALLEN 433.701585
SQL> select ename,add_months(hiredate,3) from emp;
ENAME ADD_MONTHS
---------- ----------
SMITH 1981-03-17
ALLEN 1981-05-20
WARD 1981-05-22
SQL> select next_day(sysdate,'month') from dual;
NEXT_DAY(S
----------
2017-04-17
SQL> select to_char(sysdate,'day') from dual;
TO_CHAR(SYSDATE,'DAY')
------------------------------------
monday
SQL> select to_char(sysdate,'month') from dual;
TO_CHAR(SYSDATE,'MONTH')
------------------------------------
april
SQL> select to_char(sysdate,'year') from dual;
TO_CHAR(SYSDATE,'YEAR')
------------------------------------------
twenty seventeen
SQL>
SQL> select last_day(sysdate) from dual;
LAST_DAY(S
----------
2017-04-30
SQL>