操作ｏｒａｃｌｅ自带ｓｃｏｔｔ数据库

 
SELECT hiredate
FROM emp
WHERE hiredate<to_date('1982-01-01','yyyy-mm-dd')

SELECT hiredate
FROM emp
WHERE hiredate<'01-1月-82'

SELECT SYSDATE
FROM dual

SELECT sal,comm,sal*12+nvl(comm,0)*10+10000
FROM emp

SELECT sal,comm,sal*12+nvl(comm,0)*10+10000
FROM emp
WHERE comm IS NULL

FROM a,b,c
WHERE a.x=b.y
AND b.z=c.m

FROM a JOIN b
ON a.x=b.y
JOIN c
ON b.z=c.m

SELECT ename,sal
FROM emp
WHERE sal=(SELECT MAX(sal)
            FROM emp)

varchar2(20)
char(20)
create table t_emp(empno number(4),
ename varchar2(20),
hiredate date default sysdate,
sal number(7,2))

序列
INSERT INTO copy_emp (empno,ename)
VALUES (seq1.NEXTVAL,'hhh')；

SELECT seq1.CURRVAL FROM dual；