1.TRIM函数，去掉字段中的0，如下所示
select employee_id,to_char(trim(leading 0 from hire_date)) from employees where department_id=60;select employee_id,to_char(trim(trailing 0 from hire_date)) from employees where department_id=60;select employee_id,to_char(trim(both 0 from hire_date)) from employees where department_id=60;
2.SUBSTR函数，截取字符串SQL> SELECT SUBSTR('ABCDEFG',3,4) "Substring" 2 FROM DUAL;
Subs----CDEF
SQL> SELECT SUBSTR('ABCDEFG',-5,4) "Substring" 2 FROM DUAL;
Subs----CDEF
SQL> SELECT SUBSTRB('ABCDEFG',5,4.2) "Substring with bytes" 2 FROM DUAL;
Sub---EFG
3.exit和return的用法exit用来跳出循环，用在循环中：
loop
IFA>0 THEN
EXIT;
END IF;
end loop;

return跳出存储过程，结束执行当前的过程
IF A>0 THEN
return;
END IF;

4.instr函数:计算子串在主串中的位置，其中，最后2位是可选的，如下例中的每一个，如果3，2这2个参数没有，代表的意思就是，从第一个字符开始查找第一个'OR'的位置。SELECT INSTR('CORPORATE FLOOR','OR', 3, 2) "Instring" FROM DUAL;SELECT INSTR('CORPORATE FLOOR','OR', -3, 2)"Reversed Instring" FROM DUAL;SELECT INSTRB('CORPORATE FLOOR','OR',5,2) "Instring in bytes" FROM DUAL;
5.TRUNC(number|date)如下:对于日期，如果要求到year，那么相当于为本年的1月1日开始，如果要求到mon,那么相当于为本月的1日开始；而对于数据而言，是分正负的，正数表示向小数点右边取，负数表示向小数点左边取数。SELECT TRUNC(TO_DATE('27-OCT-92','DD-MON-YY'), 'YEAR') "New Year" FROM DUAL;New Year---------01-JAN-92SELECT TRUNC(TO_DATE('27-OCT-92','DD-MON-YY'), 'MON') "New Year" FROM DUAL;
New Year---------01-OCT-92
select TRUNC(89.985,2) from dual;
TRUNC(89.985,2)--------------- 89.98SQL> select TRUNC(89.985) from dual;
TRUNC(89.985)------------- 89
SQL> select TRUNC(89.985,0) from dual;
TRUNC(89.985,0)--------------- 89SQL> select TRUNC(89.985,-1) from dual;
TRUNC(89.985,-1)---------------- 80
6.power(a,b)，求a的b次方，须注意，负数也是可以求N次方的。SELECT POWER(3,2) "Raised" FROM DUAL;
Raised---------- 9select power(10,-2) from dual;
POWER(10,-2)------------ .01