oracle函数的格式:
create or replace function 自定义函数名[(参数)]
    return 返回值类型
    is
        返回值 返回值类型
    begin
        操作
    end;

测试:
传入以个empno,获得他的用户名,
CREATE OR REPLACE
FUNCTION FUN_SEL(AA EMP.EMPNO%TYPE) RETURN VARCHAR2 AS
E_NAME EMP.ENAME%TYPE;
BEGIN
SELECT ENAME INTO E_NAME FROM EMP WHERE EMPNO=AA;
    RETURN E_NAME;
END FUN_SEL;

在sqlplus中调用函数代码:

SQL> var put varchar2(100)
SQL> exec :put:=fun_sel(7861);
PL/SQL procedure successfully completed
put
---------
tom
SQL> print put;
put
---------
tom