sql - Oracle SQL 日期间查询

Question

我不明白为什么我的查询没有返回任何内容:

 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); 

请帮我理解。谢谢你。

Answer 1

正如评论中已经提到的，您需要使用 RR格式as documented here ，或者可能更好，使用 4 位数年份。 Wernfried给出的例子在评论中:

to_date ('01/01/81', 'mm/dd/rr')

to_date ('01/01/1981', 'mm/dd/yyyy')

但是，如果您真的不需要进行任何格式化，我强烈建议您不要使用 Oracle 的格式化功能。改写这个:

select * from emp 
where hiredate between date '1981-01-01' and date '1981-12-31';

以上是 SQL 标准的日期字面量表达方式，Oracle 也支持。它比格式化字符串更容易记住，并且它独立于您的区域设置/语言等。

如果你想对时间戳做同样的事情，也有时间戳文字:

where hiredate between timestamp '1981-01-01 00:00:00.0'
                   and timestamp '1981-12-31 23:59:59.999'