我不明白为什么我的查询未返回任何内容:
select * from emp where hiredate between to_date ('01/01/81',
'mm/dd/yy') and to_date ('12/31/81', 'mm/dd/yy');
这是表格的结构:
CREATE TABLE EMP (
EMPNO NUMBER(4) NOT NULL,
ENAME CHAR(10),
JOB CHAR(9),
MGR NUMBER(4) CONSTRAINT EMP_SELF_KEY
REFERENCES EMP (EMPNO),
HIREDATE DATE,
SAL NUMBER(7,2),
COMM NUMBER(7,2),
DEPTNO NUMBER(2) NOT NULL,
CONSTRAINT EMP_FOREIGN_KEY FOREIGN KEY (DEPTNO) REFERENCES DEPT (DEPTNO),
CONSTRAINT EMP_PRIM_KEY PRIMARY KEY (EMPNO));
INSERT INTO EMP VALUES (7839,'KING','PRESIDENT',NULL,'17-NOV-1981',5000,NULL,10);
INSERT INTO EMP VALUES (7698,'BLAKE','MANAGER',7839,'1-MAY-1981',2850,NULL,30);
INSERT INTO EMP VALUES (7782,'CLARK','MANAGER',7839,'9-JUN-1981',2450,NULL,10);
INSERT INTO EMP VALUES (7566,'JONES','MANAGER',7839,'2-APR-1981',2975,NULL,20);
INSERT INTO EMP VALUES (7654,'MARTIN','SALESMAN',7698,'28-SEP-1981',1250,1400,30);
INSERT INTO EMP VALUES (7499,'ALLEN','SALESMAN',7698,'20-FEB-1981',1600,300,30);
INSERT INTO EMP VALUES (7844,'TURNER','SALESMAN',7698,'8-SEP-1981',1500,0,30);
INSERT INTO EMP VALUES (7900,'JAMES','CLERK',7698,'3-DEC-1981',950,NULL,30);
INSERT INTO EMP VALUES (7521,'WARD','SALESMAN',7698,'22-FEB-1981',1250,500,30);
INSERT INTO EMP VALUES (7902,'FORD','ANALYST',7566,'3-DEC-1981',3000,NULL,20);
INSERT INTO EMP VALUES (7369,'SMITH','CLERK',7902,'17-DEC-1980',800,NULL,20);
INSERT INTO EMP VALUES (7788,'SCOTT','ANALYST',7566,'09-DEC-1982',3000,NULL,20);
INSERT INTO EMP VALUES (7876,'ADAMS','CLERK',7788,'12-JAN-1983',1100,NULL,20);
INSERT INTO EMP VALUES (7934,'MILLER','CLERK',7782,'23-JAN-1982',1300,NULL,10);
请帮助我理解。谢谢你。
OP中声明的另一个困难
select * from emp where hiredate between to_date ('01/01/81',
'mm/dd/yy') and to_date ('12/31/81', 'mm/dd/yy');
是hiredate
可以包含一个时间的一部分。在没有样本数据的情况下,没有,但是没有什么可以阻止其发生的。考虑到这一点,下面是一个比使用更好的方法BETWEEN
:
SELECT * FROM emp
WHERE hiredate >= DATE'1981-01-01'
AND hiredate < DATE'1982-01-01';
一个人也可以使用TRUNC()
:
SELECT * FROM emp
WHERE TRUNC(hiredate, 'YEAR') = DATE'1981-01-01';
我TO_DATE()
现在看不出有任何理由使用Oracle支持ANSI日期文字(自9i开始)。
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